1

Current situation:
When you change a application's language, you obtain a message telling some like this:

The language for this application has been changed. The change will take effect the next time the application is started.

It's OK, but if you are changing language because, whatever reason is, you are in a language you don't speak, a message like that would be nothing for you.

My suggestion:
I think a message in both languages (the current language and the new language) would be more suitable because if you select a new language it may be because you speak and know that language.