Improve plural handling for code using Qt translation system

- Always load "en" translation: This way if a plural string is not translated,
  we fallback to the correct english plural form.

- Generate .ts files with correct plural settings

REVIEW: 117629

2 files changed, 15 insertions, 11 deletions

diff --git a/modules/ECMCreateQmFromPoFiles.cmake b/modules/ECMCreateQmFromPoFiles.cmake
index 3da31940..f331460d 100644
--- a/modules/ECMCreateQmFromPoFiles.cmake
+++ b/modules/ECMCreateQmFromPoFiles.cmake
@@ -134,7 +134,7 @@ function(_ECM_QM_CREATE_TARGET install_destination catalog_name)
         # strings. Finally run lrelease to create the .qm files.
         add_custom_command(OUTPUT ${qmfile}
             COMMAND ${lconvert_executable}
-                ARGS -i ${it} -o ${tsfile}
+                ARGS -i ${it} -o ${tsfile} -target-language ${language}
             COMMAND Qt5::lrelease
                 ARGS -compress -removeidentical -silent ${tsfile} -qm ${qmfile}
             DEPENDS ${it}
diff --git a/modules/ECMQmLoader.cpp.in b/modules/ECMQmLoader.cpp.in
index fd530602..2d8531f3 100644
--- a/modules/ECMQmLoader.cpp.in
+++ b/modules/ECMQmLoader.cpp.in
@@ -10,32 +10,36 @@
 
 #include <QDebug>
 
-static QTranslator *createTranslator(const QString &localeDirName)
+static bool loadTranslation(const QString &localeDirName)
 {
     QString subPath = QStringLiteral("locale/") + localeDirName + QStringLiteral("/LC_MESSAGES/@catalog_name@.qm");
     QString fullPath = QStandardPaths::locate(QStandardPaths::GenericDataLocation, subPath);
     if (fullPath.isEmpty()) {
-        return 0;
+        return false;
     }
     QTranslator *translator = new QTranslator(QCoreApplication::instance());
     if (!translator->load(fullPath)) {
         delete translator;
-        return 0;
+        return false;
     }
-    return translator;
+    QCoreApplication::instance()->installTranslator(translator);
+    return true;
 }
 
 static void load()
 {
+    // The way Qt translation system handles plural forms makes it necessary to
+    // have a translation file which contains only plural forms for `en`. That's
+    // why we load the `en` translation unconditionally, then load the
+    // translation for the current locale to overload it.
+    loadTranslation(QStringLiteral("en"));
+
     QLocale locale = QLocale::system();
-    QTranslator *translator = createTranslator(locale.name());
-    if (!translator) {
-        translator = createTranslator(locale.bcp47Name());
-        if (!translator) {
-            return;
+    if (locale.name() != QStringLiteral("en")) {
+        if (!loadTranslation(locale.name())) {
+            loadTranslation(locale.bcp47Name());
         }
     }
-    QCoreApplication::instance()->installTranslator(translator);
 }
 
 Q_COREAPP_STARTUP_FUNCTION(load)