[NEW] Informal German translations (#9984)

* Provide a dedicated informal german language option

* Use a "virtual" language code de-IN for informal german
The IETF language specification compliant suffix "informal"  did not work with the i18n library used

packages/tap-i18n/lib/plugin/etc/language_names.js

@@ -46,6 +46,8 @@ language_names = {
 	gl: ['Galician', 'Galego'],
 	ka: ['Georgian', 'ქართული'],
 	de: ['German', 'Deutsch'],
+	'de-AT': ['German (Austria)', 'Östereichisches Deutsch'],
+	'de-IN': ['German (informal)', 'Deutsch (informell)'],
 	el: ['Greek', 'Ελληνικά'],
 	gn: ['Guaraní', 'Avañe\'ẽ'],
 	haw: ['Hawaiian', 'Ōlelo Hawaiʻi'],