Selettore lingua (System/EN/IT) nelle impostazioni con QTranslator in main.cpp (pattern quill); fix 'Close book' con pop fino alla prima pagina

src/settings.cpp

@@ -152,6 +152,20 @@ void Settings::setReaderMarginV(int value)
     emit readerMarginVChanged();
 }
 
+QString Settings::language() const
+{
+    return m_settings.value(QStringLiteral("language"), QStringLiteral("system")).toString();
+}
+
+void Settings::setLanguage(const QString &value)
+{
+    if (value == language())
+        return;
+    m_settings.setValue(QStringLiteral("language"), value);
+    m_settings.sync();
+    emit languageChanged();
+}
+
 QString Settings::downloadDir() const
 {
     QString dir = QStandardPaths::writableLocation(QStandardPaths::DownloadLocation);