FEATURE: Setting preferred locale and fallback manually

lang/lang.go

@@ -7,6 +7,7 @@ import (
 	"embed"
 	"encoding/json"
 	"log"
+	"sort"
 	"strings"
 	"text/template"
 
@@ -35,6 +36,12 @@ var (
 	// More info available on the `LocalizePluralKey` function.
 	XN = LocalizePluralKey
 
+	// This defines an order in which it will try to find a fallback in case localizer does not find a match.
+	// All other languages will be in alphabetical order.
+	languageOrder = []string{"en"}
+
+	preferredLanguage string
+
 	bundle    *i18n.Bundle
 	localizer *i18n.Localizer
 
@@ -159,6 +166,21 @@ func AddTranslationsFS(fs embed.FS, dir string) (retErr error) {
 	return retErr
 }
 
+// SetLanguageOrder allows an app to set the order in which translations are checked in case no locale matches.
+// Since 2.6
+func SetLanguageOrder(order []string) {
+	languageOrder = order
+	updateLocalizer()
+}
+
+// SetPreferredLocale allows an app to set the preferred locale for translations, overwriting the System Locale.
+// locale can be in format en_US_someVariant, en_US, en-US-someVariant, en-US, en
+// Since 2.6
+func SetPreferredLocale(locale string) {
+	preferredLanguage = locale
+	updateLocalizer()
+}
+
 func addLanguage(data []byte, name string) error {
 	f, err := bundle.ParseMessageFileBytes(data, name)
 	translated = append(translated, f.Tag)
@@ -169,7 +191,6 @@ func init() {
 	bundle = i18n.NewBundle(language.English)
 	bundle.RegisterUnmarshalFunc("json", json.Unmarshal)
 
-	translated = []language.Tag{language.Make("en")} // the first item in this list will be the fallback if none match
 	err := AddTranslationsFS(translations, "translations")
 	if err != nil {
 		fyne.LogError("Error occurred loading built-in translations", err)
@@ -187,18 +208,52 @@ func fallbackWithData(key, fallback string, data any) string {
 	return str.String()
 }
 
+func orderLanguages(a, b language.Tag) bool {
+	indexA := -1
+	indexB := -1
+	for i, l := range languageOrder {
+		if a.String() == l {
+			indexA = i
+		}
+		if b.String() == l {
+			indexB = i
+		}
+	}
+	// Order both languages as defined in languageOrder
+	if indexA != -1 && indexB != -1 {
+		return indexA < indexB
+	}
+	// If it is the only language in languageOrder, it comes first
+	if indexA != -1 {
+		return true
+	}
+	if indexB != -1 {
+		return false
+	}
+	// If no language is in languageOrder, sort alphabetically
+	return strings.Compare(a.String(), b.String()) < 0
+}
+
 // A utility for setting up languages - available to unit tests for overriding system
 func setupLang(lang string) {
 	localizer = i18n.NewLocalizer(bundle, lang)
 }
 
 // updateLocalizer Finds the closest translation from the user's locale list and sets it up
 func updateLocalizer() {
+	// Sort the translated slice using the orderLanguages function
+	sort.SliceStable(translated, func(i, j int) bool {
+		return orderLanguages(translated[i], translated[j])
+	})
+
 	all, err := locale.GetLocales()
 	if err != nil {
 		fyne.LogError("Failed to load user locales", err)
 		all = []string{"en"}
 	}
+	if preferredLanguage != "" {
+		all = []string{preferredLanguage}
+	}
 	str := closestSupportedLocale(all).LanguageString()
 	setupLang(str)
 	localizer = i18n.NewLocalizer(bundle, str)

lang/lang_test.go

@@ -23,11 +23,6 @@ func TestAddTranslations(t *testing.T) {
 	assert.Equal(t, "Match2", L("Test2"))
 }
 
-func TestLocalize_Default(t *testing.T) {
-	fallback := closestSupportedLocale([]string{"xx"})
-	assert.Equal(t, fyne.Locale("en"), fallback[0:2])
-}
-
 func TestLocalize_Fallback(t *testing.T) {
 	assert.Equal(t, "Missing", L("Missing"))
 }
@@ -81,3 +76,31 @@ func TestLocalizePluralKey_Fallback(t *testing.T) {
 	assert.Equal(t, "Apple", XN("appleID", "Apple", 1))
 	assert.Equal(t, "Apples", XN("appleID", "Apple", 2))
 }
+
+func TestSetPreferredLocale(t *testing.T) {
+	_ = AddTranslations(fyne.NewStaticResource("en.json", []byte(`{
+  "Test": "Match"
+}`)))
+	_ = AddTranslations(fyne.NewStaticResource("fr.json", []byte(`{
+  "Test2": "Match2"
+}`)))
+	setupLang("fr")
+	assert.Equal(t, "Match2", L("Test2"))
+	SetPreferredLocale("en")
+	assert.Equal(t, "Match", L("Test"))
+}
+
+func TestSetLanguageOrder(t *testing.T) {
+	_ = AddTranslations(fyne.NewStaticResource("en.json", []byte(`{
+  "Test": "Match"
+}`)))
+	_ = AddTranslations(fyne.NewStaticResource("fr.json", []byte(`{
+  "Test2": "Match2"
+}`)))
+	setupLang("en")
+	SetPreferredLocale("xyz") // invalid language to test fallback
+	SetLanguageOrder([]string{"fr", "en"})
+	assert.Equal(t, "Match2", L("Test2"))
+	SetLanguageOrder([]string{"en", "fr"})
+	assert.Equal(t, "Match", L("Test"))
+}