YACReader 10: Support explicit language selection in YACReader and YACReaderLibrary

AGENTS.md

@@ -17,6 +17,40 @@ Build options:
 - `BUILD_SERVER_STANDALONE=ON`: builds only `YACReaderLibraryServer` (headless), requires only Qt 6.4+
 - `BUILD_TESTS=ON` (default): enables the test suite
 
+## Translations
+
+Use CMake translation targets (Qt LinguistTools integration), not ad-hoc `lupdate` calls.
+
+Update `.ts` files from source code (C++ + QML):
+
+```bash
+cmake --build build --target update_translations
+```
+
+On multi-config generators (Visual Studio / Ninja Multi-Config), include config:
+
+```bash
+cmake --build build --config Release --target update_translations
+```
+
+Build `.qm` files:
+
+```bash
+cmake --build build --target release_translations
+```
+
+Multi-config variant:
+
+```bash
+cmake --build build --config Release --target release_translations
+```
+
+Important:
+- Do not run `lupdate` only on `qml.qrc` (or only on a subset of files), because that can mark unrelated translations as obsolete.
+- In `YACReaderLibrary`, `qt_add_translations(...)` is configured to scan full target sources and include QML from `qml.qrc`.
+- `update_translations` updates both locale TS files and `*_source.ts` template files for all apps.
+- `*_source.ts` files are translator base templates and must not be treated as shipped locales.
+
 ## Tests
 
 ```bash

CHANGELOG.md

@@ -13,6 +13,7 @@ Version counting is based on semantic versioning (Major.Feature.Patch)
 * Migrate Flow implementation from OpenGL to QRhi. This is a full new implementation with better performance and compatibility with operating systems and hardware.
 * Add light/dark themes support that follow the system configuration.
 * Add a theme editor and support for custom themes.
+* Add an application language setting with a system default option in YACReader and YACReaderLibrary.
 
 ## 9.16.4
 

YACReader/CMakeLists.txt

@@ -79,6 +79,7 @@ qt_add_translations(YACReader
         yacreader_zh_TW.ts
         yacreader_zh_HK.ts
         yacreader_it.ts
+        yacreader_source.ts
         yacreader_en.ts
 )
 

YACReader/main.cpp

@@ -1,6 +1,5 @@
 #include <QApplication>
 #include <QDir>
-#include <QTranslator>
 #include <QCommandLineParser>
 #include <QImageReader>
 
@@ -10,6 +9,7 @@
 #include "appearance_configuration.h"
 #include "theme_manager.h"
 #include "theme_repository.h"
+#include "app_language_utils.h"
 #include "yacreader_global.h"
 
 #include "QsLog.h"
@@ -175,13 +175,8 @@ int main(int argc, char *argv[])
     logger.addDestination(std::move(debugDestination));
     logger.addDestination(std::move(fileDestination));
 
-    QTranslator translator;
-#if defined Q_OS_UNIX && !defined Q_OS_MACOS
-    translator.load(QLocale(), "yacreader", "_", QString(DATADIR) + "/yacreader/languages");
-#else
-    translator.load(QLocale(), "yacreader", "_", "languages");
-#endif
-    app.installTranslator(&translator);
+    QSettings uiSettings(YACReader::getSettingsPath() + "/YACReader.ini", QSettings::IniFormat);
+    YACReader::UiLanguage::applyLanguage("yacreader", uiSettings.value(UI_LANGUAGE).toString());
     auto mwv = new MainWindowViewer();
 
     // some arguments need to be parsed after MainWindowViewer creation

YACReader/options_dialog.cpp

@@ -17,6 +17,7 @@
 #include "theme_manager.h"
 #include "theme_factory.h"
 #include "appearance_tab_widget.h"
+#include "app_language_utils.h"
 
 #include "yacreader_spin_slider_widget.h"
 #include "yacreader_3d_flow_config_widget.h"
@@ -40,6 +41,19 @@ OptionsDialog::OptionsDialog(QWidget *parent)
     path->addWidget(pathFindButton = new QPushButton(""));
     pathBox->setLayout(path);
 
+    auto *languageBox = new QGroupBox(tr("Language"));
+    auto *languageLayout = new QHBoxLayout();
+    languageLayout->addWidget(new QLabel(tr("Application language")));
+    languageCombo = new QComboBox(this);
+    languageCombo->addItem(tr("System default"), QString());
+    const auto availableLanguages = YACReader::UiLanguage::availableLanguages("yacreader");
+    for (const auto &language : availableLanguages) {
+        languageCombo->addItem(
+                QString("%1 (%2)").arg(language.displayName, language.code), language.code);
+    }
+    languageLayout->addWidget(languageCombo);
+    languageBox->setLayout(languageLayout);
+
     QGroupBox *displayBox = new QGroupBox(tr("Display"));
     auto displayLayout = new QHBoxLayout();
     showTimeInInformationLabel = new QCheckBox(tr("Show time in current page information label"));
@@ -105,6 +119,7 @@ OptionsDialog::OptionsDialog(QWidget *parent)
     mouseModeBox->setLayout(mouseModeLayout);
 
     layoutGeneral->addWidget(pathBox);
+    layoutGeneral->addWidget(languageBox);
     layoutGeneral->addWidget(displayBox);
     layoutGeneral->addWidget(slideSizeBox);
     // layoutGeneral->addWidget(fitBox);
@@ -178,7 +193,7 @@ OptionsDialog::OptionsDialog(QWidget *parent)
     auto scaleLayout = new QVBoxLayout();
     scaleCheckbox = new QCheckBox(tr("Enlarge images to fit width/height"));
     connect(scaleCheckbox, &QCheckBox::clicked, scaleCheckbox,
-            [=](bool checked) {
+            [=, this](bool checked) {
                 Configuration::getConfiguration().setEnlargeImages(checked);
                 emit changedImageOptions();
             });
@@ -191,7 +206,7 @@ OptionsDialog::OptionsDialog(QWidget *parent)
     auto doublePageBoxLayout = new QVBoxLayout();
     coverSPCheckBox = new QCheckBox(tr("Show covers as single page"));
     connect(coverSPCheckBox, &QCheckBox::clicked, coverSPCheckBox,
-            [=](bool checked) {
+            [=, this](bool checked) {
                 settings->setValue(COVER_IS_SP, checked);
                 emit changedImageOptions();
             });
@@ -315,6 +330,12 @@ void OptionsDialog::saveOptions()
     Configuration::getConfiguration().setScalingMethod(static_cast<ScaleMethod>(scalingMethodCombo->currentIndex()));
     emit changedImageOptions();
 
+    const auto selectedLanguage = languageCombo->currentData().toString().trimmed();
+    if (selectedLanguage.isEmpty())
+        settings->remove(UI_LANGUAGE);
+    else
+        settings->setValue(UI_LANGUAGE, selectedLanguage);
+
     YACReaderOptionsDialog::saveOptions();
 }
 
@@ -326,6 +347,12 @@ void OptionsDialog::restoreOptions(QSettings *settings)
 
     pathEdit->setText(settings->value(PATH).toString());
 
+    const auto selectedLanguage = settings->value(UI_LANGUAGE).toString().trimmed();
+    int languageIndex = languageCombo->findData(selectedLanguage);
+    if (languageIndex < 0)
+        languageIndex = 0;
+    languageCombo->setCurrentIndex(languageIndex);
+
     showTimeInInformationLabel->setChecked(Configuration::getConfiguration().getShowTimeInInformation());
 
     updateColor(settings->value(BACKGROUND_COLOR, theme.viewer.defaultBackgroundColor).value<QColor>());

YACReader/options_dialog.h

@@ -29,6 +29,7 @@ class OptionsDialog : public YACReaderOptionsDialog, protected Themable
     // QLabel * pathLabel;
     QLineEdit *pathEdit;
     QPushButton *pathFindButton;
+    QComboBox *languageCombo;
 
     QCheckBox *showTimeInInformationLabel;