On wasm, use English locale if current language cannot be rendered

Chinese and Thai language characters cannot be rendered by the
default Museo font, and this is the only font bundled in the wasm
build at the moment.

For these two languages, indicate in the language list that they
are not supported in the browser, and if one of these languages are
selected as the current language, then fall back to the previously-
used application language on startup.

pages/settings/PageSettingsDisplay.qml

@@ -115,7 +115,8 @@ Page {
 
 				LanguageModel {
 					id: languageModel
-					currentLanguage: Language.current
+					//% "(no browser support)"
+					unsupportedLanguageMessage: qsTrId("settings_language_no_browser_support")
 				}
 
 				Instantiator {
@@ -133,6 +134,11 @@ Page {
 				VeQuickItem {
 					id: languageDataItem
 					uid: Global.systemSettings.serviceUid + "/Settings/Gui/Language"
+					onValueChanged: {
+						if (value !== undefined) {
+							languageModel.currentLanguage = Language.fromCode(value)
+						}
+					}
 				}
 
 				Component {

src/language.cpp

@@ -25,25 +25,44 @@ QUrl fontUrlForLanguage(QLocale::Language language)
 		{ QLocale::Thai, QStringLiteral("NotoSansThai.ttf") },
 	};
 
+	static const QUrl defaultFontUrl = QUrl("qrc:/fonts/MuseoSans-500.otf");
+
 #if defined(VENUS_WEBASSEMBLY_BUILD)
-	// On wasm, the server contains symlinks to the required font files in the root dir.
-	QString fileName = fontFileNames.value(language);
-	if (!fileName.isEmpty()) {
-		return QUrl(fileName);
-	}
+	Q_UNUSED(language);
+	// On wasm, the custom font files are not available. Just use the default font.
+	return defaultFontUrl;
+
 #elif not defined(VENUS_DESKTOP_BUILD)
 	// On device, look for the system-installed font files.
 	QString fileName = fontFileNames.value(language);
 	if (!fileName.isEmpty()) {
 		return QUrl::fromLocalFile("/usr/lib/fonts/" + fileName);
 	}
+#else
+	Q_UNUSED(language);
 #endif
 
-	// Use the default font on other platforms, or if the default font supports this language.
-	static const QUrl defaultFontUrl = QUrl("qrc:/fonts/MuseoSans-500.otf");
+	// Use the default font on other platforms.
 	return defaultFontUrl;
 }
 
+bool isLanguageRenderingSupported(QLocale::Language language)
+{
+#if defined(VENUS_WEBASSEMBLY_BUILD)
+	// On wasm, the scripts for these languages cannot be rendered by the default Museo font.
+	switch (language) {
+	case QLocale::Chinese:
+	case QLocale::Thai:
+		return false;
+	default:
+		break;
+	}
+#else
+	Q_UNUSED(language);
+#endif
+	return true;
+}
+
 }
 
 
@@ -109,7 +128,32 @@ QString LanguageModel::currentDisplayText() const
 	if (m_currentIndex < 0 || m_currentIndex >= m_languages.count()) {
 		return QString();
 	}
-	return m_languages.at(m_currentIndex).name;
+	const LanguageData &data = m_languages.at(m_currentIndex);
+	return languageDisplayName(data.language, data.name);
+}
+
+QString LanguageModel::unsupportedLanguageMessage() const
+{
+	return m_unsupportedLanguageMessage;
+}
+
+void LanguageModel::setUnsupportedLanguageMessage(const QString &msg)
+{
+	if (m_unsupportedLanguageMessage != msg) {
+		m_unsupportedLanguageMessage = msg;
+		emit unsupportedLanguageMessageChanged();
+
+		if (!isLanguageRenderingSupported(m_currentLanguage)) {
+			emit currentDisplayTextChanged();
+		}
+
+		for (int i = 0; i < m_languages.count(); ++i) {
+			if (!isLanguageRenderingSupported(m_languages.at(i).language)) {
+				static const QList<int> roles = { Qt::DisplayRole };
+				emit dataChanged(createIndex(i, 0), createIndex(i, 0), roles);
+			}
+		}
+	}
 }
 
 int LanguageModel::languageAt(int index) const
@@ -147,7 +191,7 @@ QVariant LanguageModel::data(const QModelIndex &index, int role) const
 
 	switch (role) {
 	case Qt::DisplayRole:
-		return data.name;
+		return languageDisplayName(data.language, data.name);
 	case FontFileUrlRole:
 		return data.fontFileUrl;
 	case FontFamilyRole:
@@ -157,11 +201,30 @@ QVariant LanguageModel::data(const QModelIndex &index, int role) const
 	}
 }
 
-void LanguageModel::addLanguage(const QString &name, const QString &code, const QLocale::Language &language)
+void LanguageModel::addLanguage(const QString &name, const QString &code, QLocale::Language language)
 {
 	m_languages.append({name, code, fontUrlForLanguage(language), QString(), language });
 }
 
+QString LanguageModel::languageDisplayName(QLocale::Language language, const QString &name) const
+{
+#if defined(VENUS_WEBASSEMBLY_BUILD)
+	// For languages that cannot be rendered by the default font in wasm, show the language name
+	// in English, so that the name can be rendered.
+	switch (language) {
+	case QLocale::Chinese:
+		return QStringLiteral("Chinese %1").arg(m_unsupportedLanguageMessage);
+	case QLocale::Thai:
+		return QStringLiteral("Thai %1").arg(m_unsupportedLanguageMessage);
+	default:
+		break;
+	}
+#else
+	Q_UNUSED(language);
+#endif
+	return name;
+}
+
 QHash<int, QByteArray> LanguageModel::roleNames() const
 {
 	return m_roleNames;
@@ -174,7 +237,7 @@ Language* Language::create(QQmlEngine *, QJSEngine *)
 	return language;
 }
 
-Language::Language(QQmlEngine* engine) : QObject(nullptr)
+Language::Language(QQmlEngine*) : QObject(nullptr)
 {
 	/* Load appropriate translations for current locale, e.g. :/i18n/venus-gui-v2_fr.qm */
 	if (!installTranslatorForLanguage(QLocale().language())) {
@@ -228,6 +291,14 @@ void Language::setCurrentLanguageCode(const QString &code)
 
 bool Language::installTranslatorForLanguage(QLocale::Language language)
 {
+#if defined(VENUS_WEBASSEMBLY_BUILD)
+	if (!isLanguageRenderingSupported(language)) {
+		qCWarning(venusGui) << "Cannot render language" << QLocale(language).name()
+				   << "with the default font on WASM";
+		return false;
+	}
+#endif
+
 	const bool alreadyLoaded = m_loadedTranslators.contains(language);
 	QTranslator *currTranslator = m_loadedTranslators.value(m_currentLanguage);
 	QTranslator *translator = alreadyLoaded ? m_loadedTranslators.value(language) : new QTranslator(this);

src/language.h

@@ -30,6 +30,7 @@ class LanguageModel : public QAbstractListModel
 	Q_PROPERTY(int currentIndex READ currentIndex NOTIFY currentIndexChanged)
 	Q_PROPERTY(QString currentDisplayText READ currentDisplayText NOTIFY currentDisplayTextChanged)
 	Q_PROPERTY(int count READ rowCount CONSTANT)
+	Q_PROPERTY(QString unsupportedLanguageMessage READ unsupportedLanguageMessage WRITE setUnsupportedLanguageMessage NOTIFY unsupportedLanguageMessageChanged)
 
 public:
 	enum Role {
@@ -42,9 +43,13 @@ class LanguageModel : public QAbstractListModel
 
 	int currentLanguage() const;
 	void setCurrentLanguage(int language);
+
 	int currentIndex() const;
 	QString currentDisplayText() const;
 
+	QString unsupportedLanguageMessage() const;
+	void setUnsupportedLanguageMessage(const QString &msg);
+
 	Q_INVOKABLE int languageAt(int index) const;
 	Q_INVOKABLE void setFontFamily(const QUrl &fontUrl, const QString &fontFamily);
 
@@ -55,6 +60,7 @@ class LanguageModel : public QAbstractListModel
 	void currentLanguageChanged();
 	void currentIndexChanged();
 	void currentDisplayTextChanged();
+	void unsupportedLanguageMessageChanged();
 
 protected:
 	QHash<int, QByteArray> roleNames() const override;
@@ -68,10 +74,12 @@ class LanguageModel : public QAbstractListModel
 		QLocale::Language language;
 	};
 
-	void addLanguage(const QString &name, const QString &code, const QLocale::Language &language);
+	void addLanguage(const QString &name, const QString &code, QLocale::Language language);
+	QString languageDisplayName(QLocale::Language language, const QString &name) const;
 
 	QHash<int, QByteArray> m_roleNames;
 	QList<LanguageData> m_languages;
+	QString m_unsupportedLanguageMessage;
 	int m_currentIndex = -1;
 	QLocale::Language m_currentLanguage = QLocale::AnyLanguage;
 };