Fall back to English if there is no sensible match

lang/lang.go

@@ -169,6 +169,7 @@ 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)

lang/lang_test.go

@@ -23,6 +23,11 @@ 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"))
 }

lang/translations/base.de.json

@@ -0,0 +1,31 @@
+{
+    "Create Folder": "Erstelle Ordner",
+    "Advanced": "Erweitert",
+    "Confirm": "Bestätigen",
+    "Copy": "Kopieren",
+    "Enter filename": "Dateinamen eingeben",
+    "Error": "Fehler",
+    "File": "Datei",
+    "Folder": "Ordner",
+    "New Folder": "Neuer Ordner",
+    "No": "Nein",
+    "Quit": "Beenden",
+    "Redo": "Wiederholen",
+    "Save": "Speichern",
+    "Select all": "Alle auswählen",
+    "Show Hidden Files": "Versteckte Dateien anzeigen",
+    "Undo": "Rückgängig",
+    "Yes": "Ja",
+    "file.name": {
+        "other": "Name"
+    },
+    "file.parent": {
+        "other": "Übergeordneter Ordner"
+    },
+    "Cancel": "Abbrechen",
+    "Favourites": "Favoriten",
+    "Open": "Öffnen",
+    "Paste": "Einfügen",
+    "Cut": "Ausschneiden",
+    "OK": "OK"
+}