I’ve found Application.systemLanguage but it seems to lack some important languages.
Can I by any chance get a more precise information about the sytem language to distinguish between US and UK English as well as to be able to say that the user language is Hindi?
Application.systemLanguage picks up what the OS is set to (using GetUserDefaultLangID() on Windows). Not all languages that this Windows function can return are mapped into Unity, and Hindi is one that is not. Maybe submit a bug report saying that your application cannot distinguish between US and UK versions of English.