/****************************************************************************
**
** Copyright (C) 2019 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** GNU Free Documentation License Usage
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file. Please review the following information to ensure
** the GNU Free Documentation License version 1.3 requirements
** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
** $QT_END_LICENSE$
**
****************************************************************************/

/*!
    \page qtlinguist-index.html
    \title Qt Linguist Manual
    \ingroup qttools
    \ingroup internationalization

    \startpage {index.html}{Qt Reference Documentation}
    \nextpage Overview of the Translation Process

    \keyword Qt Linguist

    Qt provides excellent support for translating Qt C++ and Qt Quick
    applications into local languages. Release managers, translators, and
    developers can use Qt tools to accomplish their tasks.

    \l{linguist-manager.html}{Release managers} bear the overall responsibility
    for the release of the application. Typically, they coordinate the work of
    developers and translators. They can use the \e lupdate tool to synchronize
    source code and translations and the \e lrelease tool to create
    run-time translation files for use by the released application.

    \l{linguist-translators.html}{Translators} can use the \QL tool to
    translate text in applications.
    No computer knowledge beyond the ability to start a program and
    use a text editor or word processor is required.

    \l{linguist-programmers.html}{Developers} must create Qt applications that are
    able to use translated text. They should also help translators identify
    the context in which phrases appear. Developers can use tutorials to learn
    about their tasks.

    For more information about the supported languages and writing systems, see
    \l{Internationalization with Qt}.

    \section1 Table of Contents

    \list
    \li \l{Overview of the Translation Process}
    \li \l{Qt Linguist Manual: Release Manager}{Release Manager}
    \li \l{Qt Linguist Manual: Translators}{Translators}
    \li \l{Qt Linguist Manual: Developers}{Developers}
    \li \l{Qt Linguist Manual: TS File Format}{TS File Format}
    \li \l{Qt Linguist Manual: Text ID Based Translations}{Text ID Based Translations}
    \li \l{CMake Commands in Qt6 LinguistTools}{CMake Commands}
    \endlist

*/

/*!
    \page linguist-overview.html
    \title Overview of the Translation Process
    \ingroup internationalization

    \previouspage Qt Linguist Manual
    \nextpage Qt Linguist Manual: Release Manager

    Most of the text that must be translated in an application
    consists of either single words or short phrases. These typically
    appear as window titles, menu items, tooltips,
    and labels to buttons, check boxes, and radio buttons.

    The phrases are entered into the source code by the developer in
    their native language using a simple but special syntax to identify
    that the phrases require translation. The Qt tools provide context
    information for each of the phrases to help the translator, and the
    developer is able to add additional context information to phrases
    when necessary.

    The release manager generates a set of translation
    files that are produced from the source files and passes these to the
    translator. The translator opens the translation files using \QL,
    enters their translations, and saves the results back into
    the translation files, which they pass back to the release manager.
    The release manager then generates fast compact versions of these
    translation files ready for use by the application.

    The tools are designed to be used in repeated cycles as applications
    change and evolve, preserving existing translations and making it
    easy to identify which new translations are required. \QL also
    provides a phrase book facility to help ensure consistent
    translations across multiple applications and projects.

    Translators and developers must address a number of issues because
    of the subtleties and complexities of human language:

    \list

    \li A single phrase may need to be translated into several
    different forms depending on context. For example, \e open in English
    might become \e{\ouml}\e{ffnen}, "open file", or \e aufbauen,
    "open internet connection", in German.

    \li Keyboard accelerators may need to be changed but without
    introducing conflicts. For example, "\&Quit" in English becomes
    "Avslutt" in Norwegian which does not contain a "Q". We cannot
    use a letter that is already in use - unless we change several
    accelerators.

    \li Phrases that contain variables, for example, "The 25 files
    selected will take 63 seconds to process", where the two numbers
    are inserted programmatically at runtime, may need to be rephrased.
    The word order in the other language may be different, so the
    variables will have to be put in another place in the sentence.

    \endlist

    The Qt translation tools provide clear and simple solutions to these
    issues.

    \QL and lupdate are able to import and export XML Localization
    Interchange File Format (XLIFF) files, making it possible to take
    advantage of tools and translation services that work with this
    format. For more information on working with these files, see
    \l{Qt Linguist Manual: Translators}{Translators}.
*/

/*!
    \page linguist-manager.html
    \title Qt Linguist Manual: Release Manager
    \ingroup internationalization

    \previouspage Overview of the Translation Process
    \nextpage Qt Linguist Manual: Translators

    Two tools are provided for the release manager: \c lupdate and
    \c lrelease. These tools can process \l {qmake Manual}{qmake} project files,
    or operate directly on the file system.

    \section1 Creating Translation Files

    Translation files consist of all the user-visible text and Ctrl key
    accelerators in an application and translations of that text.

    To create translation files:

    \list 1

        \li Run lupdate to generate the first set of translation source (TS) files
            with all the user-visible text but no translations.

        \li Give the TS files to the translator who adds translations using \QL. \QL
            takes care of any changed or deleted source text.

        \li Run lupdate to incorporate any new text added to the application.
            lupdate synchronizes the user-visible text from the application with the
            translations. It does not destroy any data.

        \li To release the application, run lrelease to read the TS files and
            produce the QM files used by the application at runtime.

    \endlist

    For \c lupdate to work successfully, it must know which translation files to
    produce. The files are listed in the application's \c .pro Qt project file.

    \target lupdate
    \section1 Using lupdate

    Usage: \c {lupdate myproject.pro}

    The lupdate command line tool finds the translatable
    strings in the specified source, header and \e {Qt Designer}
    interface files, and produces or updates \c .ts translation
    files. The files to process and the files to update can be set at
    the command line, or provided in a \c .pro file specified as a
    command line argument. The developer creates the .pro file, as
    described in \l{Qt Linguist Manual: Developers}.

    You can generate the translation file for a single QML file in
    the following way:

    \badcode
        lupdate main.qml -ts main_en.ts
    \endcode

    To make a translation file for another language, for example French,
    you copy main_en.ts to main_fr.ts, and translate the strings in the
    French TS file.

    \c lupdate processes QML files that are listed in the \c .qrc file:

    \badcode
        RESOURCES += qml.qrc
    \endcode

    To have all QML files processed by \c lupdate:

    \badcode
        lupdate application.qrc -ts myapp_en.ts
    \endcode

    You can also process all QML files without using a \c .qrc file:

    \badcode
        lupdate -extensions qml -ts myapp_en.ts
    \endcode

    If you are mostly processing QML files, but also have C++ code
    that contains strings to be translated, you can add it in the same command:

    \badcode
        lupdate qml.qrc filevalidator.cpp -ts myapp_en.ts
    \endcode

    The translation files can be mentioned in the .pro file, but it
    is also possible to do without it, and just specify the translation
    file on the command line.

    For example, to generate .ts files that will be used for English and
    French:

    \badcode
        lupdate qml.qrc filevalidator.cpp -ts myapp_en.ts myapp_fr.ts
    \endcode

    The produced translation files are given to the translator who
    uses \QL to read the files and insert the translations.

    Companies that have their own translators in-house may find it
    useful to run lupdate regularly, perhaps monthly, as the
    application develops. This will lead to a fairly low volume of
    translation work spread evenly over the life of the project and
    will allow the translators to support a number of projects
    simultaneously.

    Companies that hire in translators as required may prefer to run
    lupdate only a few times during the application life cycle. The
    first time might be just before the first test phase. This will
    provide the translator with a substantial single block of work and
    any bugs that the translator detects may easily be included with
    those found during the initial test phase. The second and any
    subsequent lupdate runs would probably take place during the
    final beta phase.

    The TS file format is a simple human-readable XML format that
    can be used with version control systems if required. \c lupdate
    can also process Localization Interchange File Format (XLIFF)
    format files; files in this format typically have file names that
    end with the \c .xlf suffix.

    \note The minimum supported version for XLIFF format files is
    1.1. XLIFF 1.0 version files are not supported.

    Pass the \c -help option to \c lupdate to view supported options.

    \QL is also able to import and export XLIFF files. See the
    \l{Qt Linguist Manual: Translators}{Translators} section for more
    information.

    \target lrelease
    \section1 Using lrelease

    Usage: \c {lrelease myproject.pro}

    The lrelease command line tool produces QM files out
    of TS files. The QM file format is a compact binary format
    that is used by the localized application. It provides extremely
    fast lookups for translations. The TS files lrelease
    processes can be specified at the command line, or given
    indirectly by a Qt \c .pro project file.

    This tool is run whenever a release of the application is to be
    made, from initial test version through to final release
    version. If the QM files are not created, for example because an
    alpha release is required before any translation has been
    undertaken, the application will run perfectly well using the text
    the developers placed in the source files. Once the QM files
    are available the application will detect them and use them
    automatically.

    \c lrelease can be also be run without specifying a \.pro file:

    \badcode
        lrelease.exe main_en.ts languages\main_fr.ts
    \endcode

    \note The lrelease tool only incorporates translations that are
    marked as "finished". Otherwise the original text is used
    instead.

    Pass the \c -help option to \c lrelease to view supported options.

    \section1 Missing Translations

    Both lupdate and lrelease may be used with TS
    translation source files which are incomplete. Missing
    translations will be replaced with the native language phrases at
    runtime.
*/

/*!
    \page linguist-translators.html
    \title Qt Linguist Manual: Translators
    \ingroup internationalization

    \previouspage Qt Linguist Manual: Release Manager
    \nextpage Qt Linguist Manual: Developers

    \QL is a tool for adding translations to Qt applications. Once you have
    installed Qt, you can start \QL in the same way as any other application on
    the development host.

    The \QL main window contains a menu bar and the following views:

    \list

        \li \gui Context (\key F6) for selecting from a list of contexts in
            which strings to be translated appear.

        \li \gui Strings (\key F7) for viewing translatable strings found in a
            context.

        \li \gui {Sources and Forms} (\key F9) for viewing the context where the
            current string is used if the source code for the context is
            accessible.

        \li Translation area for translating strings.

        \li \gui {Phrases and Guesses} (\key F10) for viewing possible
            translations for the current string.

        \li \gui Warnings (\key F8) for viewing translated strings that fail
            validation tests.

    \endlist

    \image linguist-linguist.png "Qt Linguist UI"

    The translation area (1) is always visible. To show or hide the other views,
    select \gui View > \gui Views, or use the keyboard shortcuts listed above.
    You can drag the views by their title bars and arrange them around the
    translation area or even outside the main window.

    \section1 Translating Strings

    You open translation source (TS) files in \QL for translation. TS files are
    human-readable XML files containing source phrases and their translations.
    TS files are usually created and updated by lupdate. If you do not have a TS
    file, see \l {Qt Linguist Manual: Release Manager} {Release Manager} to
    learn how to generate one.

    You can use \QL also to translate files in the international XML
    Localization Interchange File Format (XLIFF) that are generated by other
    programs. However, for standard Qt projects, only the TS file format is
    used. The minimum supported version for XLIFF format files is 1.1.

    \QL displays the target language in the translation area, and adapts the
    number of input fields for plural forms accordingly. When you open several
    TS files to translate simultaneously, the \gui Translator and
    \gui {Translator comment} fields are displayed for each language.
    For more information about setting the location information, see
    \l{Changing the Target Locale}.

    If the developer provides a \l{QObject::tr()} {disambiguating
    comment}, it is displayed in the \gui {Developer comments} field.

    To translate strings:

    \list 1

        \li Select \gui File > \gui Open to load a TS file.

        \li Select a context in the \gui Context view to load the translatable
            strings found in that context into the \gui Strings view.

        \li Select a string to copy it as the \gui {Source text} in the
            translation area. The whitespace within the source text is
            visualized so that you can see the spacing required within the text.

        \li Enter the translation of the current string in the \gui Translation
            field.

            You can also select an existing translation from the
            \gui {Phrases and Guesses} view by double-clicking it. The phrases
            are read from phrase books and the guesses are existing translations
            of similar phrases in the TS file.

        \li Optionally, enter a comment to be read by other translators in the
            \gui {Translator comment} field.

        \li To accept the translation, press \key {Ctrl+Enter}, select
            \inlineimage linguist-doneandnext.png
            , or click the icon to the left of the selected source string in the
            string list.

        \li Select \gui File > \gui Save to save your work.

    \endlist

    Repeat this process until all strings in the string list are marked with
    \inlineimage linguist-check-on.png
    (\gui {Accepted/Correct}) or
    \inlineimage linguist-check-warning.png
    (\gui {Accepted/Warnings}). Then select the next context and continue.

    To view the number of words and characters in the source text and in the
    translated text, select \gui View > \gui Statistics.

    Select \gui File > \gui Release to create a Qt message QM file with the same
    base name as the current translation source file. The release manager's
    command line tool lrelease performs the same function on \e all of an
    application's translation source files.

    To print the translation source and the translations, select \gui File >
    \gui Print.

     To quit \QL, select \gui File > \gui Exit.

    \section2 Leaving a Translation for Later

    If you wish to leave a translation, press \key{Ctrl+L} (Next
    Unfinished) to move to the next unfinished translation. To move to
    the next translation (whether finished or unfinished) press
    \key{Shift+Ctrl+L}. You can also navigate using the \gui Translation
    menu. If you want to go to a different context entirely, click the
    context you want to work on in the \gui Context list, then click the
    source text in the \gui Strings view.

    \section2 Phrases That Require Multiple Translations Depending on Context

    The same phrase may occur in two or more contexts without conflict. Once
    a phrase has been translated in one context, \QL notes that the translation
    has been made and when the translator reaches a later occurrence of the same
    phrase, \QL provides
    the previous translation as a possible translation candidate in the
    \gui {Phrases and Guesses} view.

    If a phrase occurs more than once in a particular context it is shown only
    once in the \gui Context view and the translation is applied to every
    occurrence within the context. If the same phrase needs to be translated
    differently within the same context, the developer must provide a
    distinguishing comment for each occurrence of the phrase. If such comments
    are used, the duplicate phrases appear in the \gui Context view. The
    developer's comments appear in the translation area on a light blue
    background.

    \section2 Changing Keyboard Accelerators

    A keyboard accelerator is a key combination that, when pressed,
    causes an application to perform an action. There are two kinds of
    keyboard accelerators: Alt key and Ctrl key accelerators.

    \section3 Alt Key Accelerators

    Alt key accelerators are used in menu selection and on buttons.
    The underlined character in a menu item or button label signifies
    that pressing the Alt key with the underlined character will
    perform the same action as clicking the menu item or pressing the
    button. For example, most applications have a \e{File} menu with
    the "F" in the word "File" underlined. In these applications the
    \e{File} menu can be invoked either by clicking the word "File" on
    the menu bar or by pressing \e{Alt+F}. To identify an accelerator
    key in the translation text ("File") precede it with an ampersand:
    \e{\&File}. If a string to be translated has an ampersand in
    it, then the translation for that string should also have an
    ampersand in it, preferably in front of the same character.

    The meaning of an Alt key accelerator can be determined from the
    phrase in which the ampersand is embedded. The translator can
    change the character part of the Alt key accelerator, if the
    translated phrase does not contain the same character or if that
    character has already been used in the translation of some other
    Alt key accelerator. Conflicts with other Alt key accelerators
    must be avoided within a context. Note that some Alt key
    accelerators, usually those on the menu bar, may apply in other
    contexts.

    \section3 Ctrl Key Accelerators

    Ctrl key accelerators can exist independently of any visual
    control. They are often used to invoke actions in menus that would
    otherwise require multiple keystrokes or mouse clicks. They may
    also be used to perform actions that do not appear in any menu or
    on any button. For example, most applications that have a \e{File}
    menu have a \e{New} submenu item in the \e{File} menu. The \e{New}
    item might appear as "\underline{N}ew Ctrl+N" in the \e{File}
    menu, meaning the \e{New} menu can be invoked by simply pressing
    \key{Ctrl+N}, instead of either clicking \e{File} with the mouse
    and then clicking \e{New} with the mouse, or by entering \e{Alt+F}
    and \e{N}.

    Each Ctrl key accelerator is shown in the \gui Strings view
    as a separate string, for example \key{Ctrl+Enter}. Since
    the string does not have a context to give it meaning, such as
    the context of the phrase in which an Alt key accelerator appears,
    the translator must rely on the UI developer to include a
    \l{QObject::tr()} {disambiguation comment} to explain the action
    the Ctrl key accelerator is meant to perform. This disambiguating
    comment (if provided by the developer) will appear under
    \gui {Developer comments} in the translation area below the
    \gui {Source text} field.

    Ideally, translations for Ctrl key accelerators are simply copied by
    selecting \gui Translation > \gui {Copy from source text}. However, in some
    cases the character will
    not make sense in the target language, and it must be
    changed. Whichever character (alpha or digit) is chosen, the
    translation must be in the form "Ctrl+" followed by the upper case
    character. Qt will automatically display the correct name at
    run-time. As with Alt key accelerators, if the translator changes
    the character, the new character must not conflict with any other
    Ctrl key accelerator.

    \warning Do not translate the "Alt", "Ctrl" or "Shift" parts of
    the accelerators. Qt relies on these strings being there. For
    supported languages, Qt automatically translates these strings.

    \section2 Handling Numbered Arguments and Plurals

    Some phrases contain numbered arguments. A numbered argument is a
    placeholder that will be replaced with text at run-time. A numbered
    argument appears in a source string as a percent sign followed by
    a digit. Consider an example: \c{After processing file %1, file %2
    is next in line}. In this string to be translated, \c{%1} and
    \c{%2} are numbered arguments. At run-time, \c{%1} and \c{%2} will
    be replaced with the first and second file names respectively. The
    same numbered arguments must appear in the translation, but not
    necessarily in the same order. A German translation of the string
    might reverse the phrases, for example \c{Datei %2 wird bearbeitet, wenn
    Datei %1 fertig ist}. Both numbered arguments appear in the
    translation, but in the reverse order. \c{%i} will always be
    replaced by the same text in the translation strings, regardless
    of where argument \e{i} appears in the argument sequence in the
    source string.

    The use of numbered arguments is often accompanied by the use of
    plurals in the source text. In many languages, the form of the
    text will depend on the value shown, and more than one translation
    is required. If the developers have marked up the source text in
    correct way, fields for each of the possible plural forms will be
    available in the translation area. For more information, see
    \l{Writing Source Code for Translation#Handling Plurals}
    {Writing Source Code for Translation}.

    \section2 Changing the Target Locale

    You can set the locale information explicitly in \gui Edit >
    \gui {Translation File Settings}. If the target language and country
    are not explicitly set when you open a translation source file, \QL
    attempts to deduct them from the translation source file name. This
    requires that the translation files adhere to the following file name
    convention:
    \c appname_language[_country].ts, where:

    \list
      \li \c language is an ISO 639 language code in lowercase.
      \li \c country is an ISO 3166 two-letter country code in uppercase.
    \endlist

    If this attempt to resolve the target language and country fails, the
    \gui {Translation File Settings} window opens.

    For example, \c app_de.ts sets the
    target language to German, and \c app_de_ch.ts sets the target language to
    German and the target country to Switzerland. This also helps loading
    translations for the current locale automatically. For more information, see
    \l{linguist-programmers.html}{Developers}.

    \image linguist-translationfilesettings.png

    \section1 Selecting Context to Translate

    The \gui Context view lists the contexts in which strings to be translated
    appear. The column labeled \gui Context lists the context names in
    alphabetical order. Each context is the name of a subclass of
    QObject. There can also be a context for QObject itself, which
    contains strings passed to the static function QObject::tr().
    There can also be an \e{<unnamed context>}, which contains strings
    that are not in a subclass of QObject.

    The following icons indicate the current translation state for each context:

    \table
    \header
    \li State
    \li Icon
    \li Description

    \row
    \li Accepted/Correct
    \li \inlineimage linguist-check-on.png
    \li  All strings in the context have been translated, and all the
        translations passed the \l{Validating Translations}{validation tests}.

    \row
    \li Accepted/Warnings
    \li \inlineimage linguist-check-warning.png
    \li All strings in the context have been translated or marked as translated,
        but at least one translation failed the validation tests.
        In the \gui Strings view, you can see which string failed the test.

    \row
    \li Not Accepted
    \li \inlineimage linguist-check-off.png
    \li At least one string in the context has not been translated or is not
        marked as translated.

    \row
    \li Obsolete
    \li \inlineimage linguist-check-obsolete.png
    \li None of the translated strings appears in the context any more. This
        usually means the context itself no longer exists in the application.
    \endtable

    The \gui Items column displays the total number of translatable strings in
    the context and the number of translated strings, separated by a slash (/).
    If the numbers are equal, all the translatable strings in the context have
    translations.

    \section1 Selecting String to Translate

    The \gui Strings view lists all the translatable strings found in the
    current context and their translation acceptance state. Selecting a string
    makes that string the current string in the translation area.

    Click the icon in front of a string to change its translation acceptance
    state. A tick mark, green or yellow, means the string has been translated
    and the translation has been accepted. A question mark means either that the
    translation has not been accepted or that the string does not have a
    translation.

    The following icons indicate the current translation state for each string:

    \target String Translation States

    \table
    \header
    \li State
    \li Icon
    \li Description

    \row
    \li Accepted/Correct
    \li \inlineimage linguist-check-on.png
    \li The source string has a translation (possibly empty). The user
        has accepted the translation, and the translation passes all the
        \l{Validating Translations} {validation tests}. If the translation is
        empty, the user has chosen to leave it empty. Click the icon to
        revoke acceptance of the translation and decrement the number of
        accepted translations in the \gui Items column of the \ gui Context view
        by 1. The state is reset to \gui {Not Accepted} if the string has a
        translation, or to \gui {No Translation} if the string's translation is
        empty. If \c{lupdate} changes the contents of a string, its acceptance
        state is automatically reset to \gui {Not Accepted}.

    \row
    \li Accepted/Warnings
    \li \inlineimage linguist-check-warning.png
    \li The user has accepted the translation, but the translation does
        not pass all the validation tests. The validation test failures are
        shown in the \gui Warnings view. Click the icon to revoke acceptance of
        the translation. The state is reset to \gui {Validation Failures}, and
        the number of accepted translations in the \gui Items column of the
        \gui Context view is decremented by 1.

    \row
    \li Not Accepted
    \li \inlineimage linguist-check-off.png
    \li The string has a translation that passes all the validation tests, but
        the user has not yet accepted the translation. Click the icon or press
        \key{Ctrl+Enter} to accept the translation. The state is reset to
        \gui {Accepted/Correct}, and the number of accepted translations in the
        \gui Items column of the \gui Context view is incremented by 1.

    \row
    \li No Translation
    \li \inlineimage linguist-check-empty.png
    \li The string does not have a translation. Click the icon to
        accept the empty translation anyway. The state is reset to
        \gui {Accepted/Correct}, and the number of accepted translations in the
        \gui Items column of the \gui Context view is incremented by 1.

    \row
    \li Validation Failures
    \li \inlineimage linguist-danger.png
    \li The string has a translation, but the translation does not pass all the
        validation tests. Validation test failures are shown in the
        \gui Warnings view. Click on the icon or press \key{Ctrl+Return} to
        accept the translation even with validation failures. The state is
        reset to \gui {Accepted/Warnings}. We recommended editing the
        translation to fix the causes of the validation failures. The state will
        reset automatically to \gui {Not Accepted}, when all the failures have
        been fixed.

    \row
    \li Obsolete
    \li \inlineimage linguist-check-obsolete.png
    \li The string is obsolete. It is no longer used in the context.
        See the \l{Qt Linguist Manual: Release Manager} {Release Manager}
        for instructions on how to remove obsolete messages from the file.

    \endtable

    \section1 Viewing Strings in Context

    If the source files containing the translatable strings are
    available to \QL, the \gui {Sources and Forms} view shows the source context
    of the current string in the \gui Strings view. The source
    code line containing the current string should be shown and
    highlighted. If the file containing the source string is not
    found, the expected absolute file path is shown.

    If the source context shows the wrong source line, it probably
    means the translation file is out of sync with the source files.
    For more information about how to re-sync the translation file with the
    source files, see \l{Using lupdate}.

    Forms created by \QD are stored in special UI files. \QL can make use of
    these UI files to show the translations done so far on the form itself if
    the UI files are available to it during the translation process.

    \section1 Reusing Translations

    If the translated text is similar to the source text, select
    \gui Translation > \gui {Copy from source text} (or press \key{Ctrl+B}) to
    copy the source text into the translation area.

    In \QL, \e {phrase books} are used to provide a common set of translations
    to help ensure consistency. A phrase book is a set of source phrases, target
    (translated) phrases, and optional definitions. Typically, one phrase book
    is created per language and family of applications. Phrase books can also be
    used to avoid duplication of effort since the translations for a family of
    applications can be produced once in the phrase book.

    If the current string in the \gui Strings view appears in one or more of the
    phrase books that have been loaded, the current string and its phrase book
    translations are listed in the \gui {Phrases and Guesses} view. If the
    current string is the same as, or similar to, another string that has
    already been translated, that other string and its translation
    are also listed in this view.

    To copy a translation from the \gui {Phrases and Guesses} view to the
    translation area, double-click it or select it and press \key Enter.

    \section2 Batch Translation

    \image linguist-batchtranslation.png

    Use the batch translation feature of \QL to automatically translate source
    texts that are also in a phrase book. To configure which phrase books to use
    in what order during the batch translation process, select \gui Edit >
    \gui {Batch Translation}. You can specify whether only entries with no
    current translation should be considered, and whether batch translated
    entries should be marked as \gui Accepted.

    \section2 Creating and Editing Phrase Books

    Phrase book files are human-readable XML files containing standard phrases
    and their translations. These files are created and updated by \QL and may
    be used by any number of projects and applications.

    To create a new phrase book, select \gui Phrases > \gui {New Phrase Book}.

    \image linguist-phrasebookdialog.png

    To open a phrase book, select \gui Phrases > \gui {Open Phrase Book}, and
    then select the Qt phrase book file (.qph) to open.

    To view and change open phrase books, select \gui Phrases >
    \gui {Edit Phrase Book}.

    To add a new phrase, select \gui {New Entry} (or press \key {Alt+N}) and
    type in a new source phrase, the translation, and an optinal definition.
    This is useful to distinguish different translations of the same source
    phrase.

    To add the translation you are working on to the current phrase book, select
    \gui Phrases > \gui {Add to Phrase Book} or press \key{Ctrl+T}. If multiple
    phrase books are loaded, you have to select one.

    If you detect an error in a phrase book entry that is shown in the
    \gui {Phrases and Guesses} view, you can also edit it in place by right
    clicking on the entry, and selecting \gui Edit. After fixing the error
    press \key{Return} to leave the editing mode.

    To delete a phrase, select it in the \gui {Source phrase} list, and then
    select \gui {Remove Entry}.

    To print an open phrase book, select \gui Phrases >
    \gui {Print Phrase Book}.

    \section1 Validating Translations

    \QL provides the following validation tests for translations:

    \list
        \li \e {Accelerator validation} detects translated phrases
            that do not have an ampersand when the source phrase does and vice
            versa.
        \li \e {Punctuation validation} detects differences in the
            terminating punctuation between source and translated phrases when
            this may be significant. For example, warns if the source phrase
            ends with an ellipsis, exclamation mark or question mark, and the
            translated phrase does not, and vice versa.
        \li \e {Phrases validation} detects source phrases that are
            also in the phrase book but whose translation differs from that
            given in the phrase book.
        \li \e {Place marker validation} detects whether the same variables
            (like \c %1, \c %2) are used both in the source text and in the
            translation.
    \endlist

    To switch validation tests on or off, select \gui Validation or use the
    toolbar buttons.

    Not accepted strings that fail validation tests are marked with the
    \gui {Validation Failures} icon in the \gui Strings view. Accepted strings
    are marked with \gui {Accepted/Warnings}.

    If you switch validation off and then switch it on later,
    \QL rechecks all phrases and marks any that fail validation.

    If the translation you enter for the current string fails any of
    the active validation tests, the failures
    are listed in the \gui Warnings view. The first of these failure
    messages is also shown in the status bar at the bottom of the main
    window.

    \note Only results of \e{active} validation tests are reported.

    \target multiple languages
    \section1 Translating Multiple Languages Simultaneously

    You can load and edit multiple translation files simultaneously.
    The following screen shot displays \e{Polish} and \e{Japanese} translation
    files loaded.

    \image linguist-linguist_2.png

    The translation area has text editing areas for both Polish and Japanese,
    and these are color-coded for easier separation. The \gui Context view and
    the \gui Strings view both have two status columns instead of one,
    color-coded with the same colors. The left-most column
    is related to the top-most language area (Polish above)
    in the translation area, and the right-most column is related to the bottom
    language area.

    The \gui Items column in the \gui Context view combines the values
    for both languages. If the number of translatable strings does not match the
    number of accepted strings, either or both languages have strings that need
    to be translated or accepted. The \gui Strings view shows the translation
    acceptance state of each string for each language.
*/

/*!
    \page linguist-programmers.html
    \title Qt Linguist Manual: Developers
    \ingroup internationalization

    \previouspage Qt Linguist Manual: Translators
    \nextpage Qt Linguist Manual: TS File Format

    Support for multiple languages is extremely simple in Qt
    applications, and adds little overhead to the developer's workload.

    Qt minimizes the performance cost of using translations by
    translating the phrases for each window as they are created. In most
    applications the main window is created just once. Dialogs are often
    created once and then shown and hidden as required. Once the initial
    translation has taken place there is no further runtime overhead for
    the translated windows. Only those windows that are created,
    destroyed and subsequently created will have a translation
    performance cost.

    Creating applications that can switch language at runtime is possible
    with Qt, but requires a certain amount of developer intervention and
    will of course incur some runtime performance cost.

    \section1 Specifying Translation Sources in Qt Project Files

    To enable release managers to use lupdate and lrelease, specify
    a \c .pro Qt project file. There must be an entry in the \c TRANSLATIONS
    section of the project file for each language that is additional to
    the native language. A typical entry looks like this:

    \snippet arrowpad/arrowpad.pro 1

    Using a locale within the translation file name is useful for
    determining which language to load at runtime. For more information, see
    QLocale.

    The \c lupdate tool extracts user interface strings from your application.
    It reads the application .pro file to identify which source files
    contain text to be translated. This means your source files must be listed
    in the \c SOURCES or \c HEADERS entry in the .pro file, or in resource
    files listed in the \c RESOURCE entry. If your files are
    not listed, the text in them will not be found.

    An example of a complete \c .pro file with four translation source
    files:

    \snippet doc_src_linguist-manual.pro 0

    \c lupdate expects all source code to be encoded in UTF-8 by default.
    Files that feature a BOM (Byte Order Mark) can also be encoded in
    UTF-16 or UTF-32. Set the qmake variable \c CODECFORSRC to
    \c UTF-16 to parse files without a BOM as UTF-16.

    Some editors, such as Visual Studio, however use a different
    encoding by default. One way to avoid encoding issues is to limit any
    source code to ASCII, and use escape sequences for translatable strings
    with other characters, for example:

    \snippet doc_src_linguist-manual.cpp 3

    \section1 Internationalizing Applications

    Design your application so that it can be adapted to various languages and
    regions without engineering changes. Qt tries to make internationalization
    as painless as possible for you. All input controls and text drawing methods
    in Qt offer built-in support for all supported languages. But you still need
    to keep the following things in mind when writing source code for your
    application:

    \list

        \li Make your application look for and load the appropriate translation
            file.

        \li Mark user-visible text and Ctrl keyboard accelerators as targets for
            translation.

        \li Provide context for text to be translated.

        \li Disambiguate identical texts.

        \li Use numbered arguments (%n) as placeholders for parameters that are
            replaced with text or numbers at run-time.

        \li Internationalize numbers, dates, times, and currencies.

        \li Mark data text strings outside functions translatable.

    \endlist

    You can develop applications that use both C++ and QML sources in the same
    application and even have user interface strings in both sources. The tools
    create a single combined translation file and the strings are accessible
    from C++ and QML.

    The classes that support internationalizing of Qt applications are described
    in \l{Internationalization with Qt}. The process of making source code
    translatable is described in \l{Writing Source Code for Translation} and in
    \l{Internationalization and Localization with Qt Quick}.

    Each piece of text that requires translating requires context to help
    the translator identify where in the program the text appears. In the
    case of multiple identical texts that require different translations,
    the translator also requires some information to disambiguate the
    source texts. Marking text for translation will automatically cause
    the class name to be used as basic context information. In some cases
    the developer may be required to add additional information to help
    the translator.

    \section1 Deploying Translations

    The \c .qm files required for the application should be placed in a
    location where the loader code using \l QTranslator can locate them.
    Typically, this is done by specifying a path relative to
    \l QCoreApplication::applicationDirPath().

    Usually, there are \c .qm files for the application, and, if a version of
    Qt is used that is not installed on the system, Qt's .qm files need to be
    deployed as well.

    In Qt 4, there is one big, monolithic \c .qm file per locale. For example,
    the file \c qt_de.qm contains the German translation of all libraries.

    In Qt 5, the \c .qm files were split up by module and there is a so-called
    meta catalog file which includes the \c .qm files of all modules. The
    name of the meta catalog file is identical to the name of Qt 4's monolithic
    \c .qm file so that existing loader code works as before provided
    all included \c .qm files are found.

    However, it is not necessary to always deploy all of Qt 5's \c .qm files.
    We recommend concatenating the \c .qm files of the modules required to
    one file matching the meta catalog file name using the tool \c lconvert in
    the deploy step. For example, to create a German translation file for an
    application using the modules \l{Qt Core}, \l {Qt GUI}, and \l {Qt Quick},
    run:

    \code
    lconvert -o installation_folder/qt_de.qm qtbase_de.qm qtdeclarative_de.qm
    \endcode

    \section1 Tutorials

    The following tutorials illustrate how to prepare Qt applications for
    translation:

    \list
    \li \l{hellotr}{Hello tr()} is a C++ application that demonstrates the
        creation of a \l QTranslator object. It also shows the simplest use of
        the \c tr() function to mark user-visible source text for
        translation.

    \li \l{arrowpad}{Arrow Pad} is a C++ application that demonstrates how to
       make the application load the
       translation file applicable to the current locale. It also shows the
       use of the two-argument form of \c tr() which provides additional
       information to the translator.

    \li \l{trollprint}{Troll Print} is a C++ application that demonstrates how
        identical source texts can be distinguished even when they occur in
        the same context. This tutorial also discusses how the translation
        tools help minimize the translator's work when an application is
        upgraded.

    \li \l{QML Examples - Internationalization}{Internationalization} is a
        Qt Quick application that demonstrates how to internationalize Qt Quick
        applications.
    \endlist
*/

/*!
    \page linguist-ts-file-format.html
    \title Qt Linguist Manual: TS File Format
    \ingroup internationalization

    \previouspage Qt Linguist Manual: Developers
    \nextpage Qt Linguist Manual: Text ID Based Translations

    The TS file format used by \QL is described by the
    \l{http://www.w3.org/TR/1998/REC-xml-19980210}{DTD} presented below,
    which we include for your convenience. Be aware that the format
    may change in future Qt releases.

    \quotefile ../../../shared/ts.dtd

*/

/*!
    \page linguist-id-based-i18n.html
    \title Qt Linguist Manual: Text ID Based Translations
    \ingroup internationalization

    \previouspage Qt Linguist Manual: TS File Format

    \brief Text ID based internationalization provides support for large scale
    projects with many target locales and many texts to translate.

    The text ID translation mechanism is an "industrial strength" system for
    internationalization and localization. Each text in the application is assigned
    a unique identifier (text ID) and these identifiers are used directly in the
    source code in place of the plain texts. This requires a little more work for
    the user interface developers but makes it much easier to manage large numbers
    of translated texts.

    \note You must use only plain-text-based or only text-ID-based functions in
    one application. If you mix them, you will end up with an incomplete set of
    texts to be translated.


    \section1 Internationalizing With Text IDs

    When using text IDs instead of plain text, the general method of
    internationalizing an application is the same but the details are a bit
    different:

    \list 1

        \li The functions and macros for the text-ID-based translation system are
        different to the plain-text system. You use the \c qsTrId() function instead
        of qsTr(), and the \c QT_TRID_NOOP() macro instead of QT_TR_NOOP().

        \li Use text IDs as user interface strings rather than plain text
        strings. For example, \c {qsTrId("id-back-not-front")}

        \li You cannot specify a context parameter with a text ID. If there are
        identically spelled words with different meanings, these need separate
        text IDs. For example, \c {qsTrId("id-back-backstep")} will
        differentiate the back-step "Back" from the back-of-the-object "Back".

        \li The "Engineering English" text that you see in the user interface for
        development builds is indicated with a \c {//%} comment. If you do not
        include this, the text ID will be shown in the user interface. This is
        especially important when you have texts with parameters. The \c {//%}
        comment needs to include the parameters indicators in the string. For
        example, \c {//% "Number of files: %1"}

        \li The \c {//:} comments that provide extra information to the translator
        are optional in the plain-text system. However, with the text-ID-based
        system, this extra information becomes essential because without it you only
        have the text ID and the translator might not be able to make a sensible
        translation from that without further context. You can use long descriptive
        text IDs and no comments, but comments are often easier to understand.

    \endlist

    The side-by-side code snippets below show a comparison of text-ID -based and
    plain-text-based translations:

    \table
        \header
            \li text-ID-based
            \li plain-text-based
        \row
            \li
            \code
            Text {
                id: backTxt;
                //: The back of the object, not the front
                //% "Back"
                //~ Context Not related to back-stepping
                text: qsTrId("id-back-not-front");
            }
            \endcode

            \li
            \code
            Text {
                id: backTxt;
                //: The back of the object, not the front
                //~ Context Not related to back-stepping
                text: qsTr("Back","Not front")
            }
            \endcode
    \endtable

    \section1 Localizing With Text IDs

    Localizing with text IDs follows much the same process as for plain text.

    The \c lupdate tool is used the same way and translations are made into
    the .ts files:

    \code
    lupdate <myapp>.pro
    \endcode

    Note that the source values in the translation files will be text IDs rather
    than plain text. This means you need very descriptive text IDs, or good
    additional comments, or both to ensure that the translator makes a correct
    translation.

    The example text-ID-based user interface text from above results in the following
    content in the .ts file:

    \code
    <message id="id-back-not-front">
        <source>Back</source>
        <extracomment>The back of the object, not the front</extracomment>
        <translation type="unfinished"></translation>
        <extra-Context>Not related to back-stepping</extra-Context>
    </message>
    \endcode

    When using \c lrelease, you need to specify that the keys for translated
    texts are based on text IDs, rather than plain texts. If strings in the code
    are specified with \c qsTr() there is no "id" attribute set so they are
    ignored by \c lrelease.

    This command produces all the compiled translation .qm files for your
    application:

    \code
    lrelease -idbased <myapp>.pro
    \endcode

    However, if there is no translation available for a given text (which is
    generally the case until late in development), the text ID will be shown in
    the user interface rather than a proper text. In order to make the application
    more usable for testing, you can make \c lrelease use the "Engineering English"
    source text (from the \c {//%} comments) as the translated text and mark it with
    some indicator so you can see texts that are not yet translated.

    For example, this command builds the .qm files and puts a "!" in front of the
    untranslated texts:

    \code
    lrelease -idbased -markuntranslated ! <myapp>.pro
    \endcode



    \section1 Advanced Usage

    For projects that target a large number of locales, you can remove the
    TRANSLATIONS info from the .pro file and, instead, manage the translations
    with a separate script. The script can call lrelease and lupdate for each of
    the desired targets.

    The updates could be scripted something like this:

    \code
    lupdate -recursive <project-dir> -ts <project-dir>/i18n/myapp-text_en_GB.ts
    lupdate -recursive <project-dir> -ts <project-dir>/i18n/myapp-text_en_US.ts
    ...
    \endcode

    The generation of the final .qm files could be scripted something like this:

    \code
    lrelease -idbased <project-dir>/i18n/myapp-text_en_GB.ts
    lrelease -idbased <project-dir>/i18n/myapp-text_en_US.ts
    ...
    \endcode

*/
