Add a setting to select the language in the options dialog

All translations have been updated, and translations of the actions in the library have been fixed.

common/app_language_utils.h

@@ -0,0 +1,131 @@
+#ifndef APP_LANGUAGE_UTILS_H
+#define APP_LANGUAGE_UTILS_H
+
+#include "yacreader_global_gui.h"
+
+#include <QCoreApplication>
+#include <QDir>
+#include <QLocale>
+#include <QRegularExpression>
+#include <QSet>
+#include <QTranslator>
+#include <algorithm>
+
+namespace YACReader::UiLanguage {
+
+struct LanguageOption {
+    QString code;
+    QString displayName;
+};
+
+inline QStringList translationDirectories()
+{
+    QStringList directories;
+#if defined(Q_OS_UNIX) && !defined(Q_OS_MACOS)
+    directories << QString(DATADIR) + "/yacreader/languages";
+#endif
+    directories << QCoreApplication::applicationDirPath() + "/languages";
+    directories.removeDuplicates();
+    return directories;
+}
+
+inline bool loadFromLocale(QTranslator &translator, const QString &prefix, const QLocale &locale)
+{
+    const auto dirs = translationDirectories();
+    for (const auto &dir : dirs) {
+        if (translator.load(locale, prefix, "_", dir))
+            return true;
+    }
+
+    return false;
+}
+
+inline bool loadTranslator(QTranslator &translator, const QString &prefix, const QString &languageOverride = QString())
+{
+    auto selectedLanguage = languageOverride.trimmed();
+    if (!selectedLanguage.isEmpty()) {
+        selectedLanguage.replace('-', '_');
+
+        if (loadFromLocale(translator, prefix, QLocale(selectedLanguage)))
+            return true;
+
+        auto baseLanguage = selectedLanguage.section('_', 0, 0);
+        if (baseLanguage != selectedLanguage && loadFromLocale(translator, prefix, QLocale(baseLanguage)))
+            return true;
+    }
+
+    return loadFromLocale(translator, prefix, QLocale());
+}
+
+inline QTranslator &appTranslator()
+{
+    static QTranslator translator;
+    return translator;
+}
+
+inline bool applyLanguage(const QString &prefix, const QString &languageOverride = QString())
+{
+    auto &translator = appTranslator();
+    QCoreApplication::removeTranslator(&translator);
+    const auto loaded = loadTranslator(translator, prefix, languageOverride);
+    QCoreApplication::installTranslator(&translator);
+    return loaded;
+}
+
+inline QString languageDisplayName(const QString &languageCode)
+{
+    QLocale locale(languageCode);
+
+    QString languageName = locale.nativeLanguageName();
+    if (languageName.isEmpty())
+        languageName = QLocale::languageToString(locale.language());
+
+    if (languageName.isEmpty())
+        languageName = languageCode;
+
+    QString territoryName;
+    if (locale.territory() != QLocale::AnyTerritory)
+        territoryName = locale.nativeTerritoryName();
+
+    if (!territoryName.isEmpty())
+        return QString("%1 (%2)").arg(languageName, territoryName);
+
+    return languageName;
+}
+
+inline QList<LanguageOption> availableLanguages(const QString &prefix)
+{
+    QSet<QString> languageCodes;
+    const auto pattern = QRegularExpression(
+            "^" + QRegularExpression::escape(prefix) + "_(.+)\\.qm$");
+
+    const auto dirs = translationDirectories();
+    for (const auto &dirPath : dirs) {
+        QDir dir(dirPath);
+        if (!dir.exists())
+            continue;
+
+        const auto files = dir.entryList(
+                QStringList { prefix + "_*.qm" }, QDir::Files, QDir::Name);
+        for (const auto &file : files) {
+            auto match = pattern.match(file);
+            if (match.hasMatch())
+                languageCodes.insert(match.captured(1));
+        }
+    }
+
+    QList<LanguageOption> options;
+    for (const auto &languageCode : languageCodes) {
+        options.append({ languageCode, languageDisplayName(languageCode) });
+    }
+
+    std::sort(options.begin(), options.end(), [](const LanguageOption &lhs, const LanguageOption &rhs) {
+        return lhs.displayName.localeAwareCompare(rhs.displayName) < 0;
+    });
+
+    return options;
+}
+
+} // namespace YACReader::UiLanguage
+
+#endif // APP_LANGUAGE_UTILS_H

common/yacreader_global_gui.h

@@ -7,6 +7,7 @@
 #include <QMimeData>
 
 #define PATH "PATH"
+#define UI_LANGUAGE "UI_LANGUAGE"
 #define MAG_GLASS_SIZE "MAG_GLASS_SIZE"
 #define MAG_GLASS_ZOOM "MAG_GLASS_ZOOM"
 #define ZOOM_LEVEL "ZOOM_LEVEL"