Problem with language recognition

Okay so I downloaded a german wow client to practice my german speaking skills while playing, everything is going fine apart from one thing:

I need to be able to type umlaut-letters (ä, ö, ü), for example when i want to throw away a blue or epic item, as well as when configuring addons.
The thing is, my keyboard is english-cyrillic, so even when I copy an umlaut letter, ingame it just shows a cyrillic letter instead (or just a "?" sign), making the use of gamebreaking addons such as healing addons (healbot, vuhdo etc) impossible in this client.

So, any idea how I could make the game differentiate between cyrillic letters and anything else that's not english? I initially thought the ingame font didn't support umlaut letters but that doesn't seem to be the case as I changed it with a font that does and the problem persists, so I'm kind of out of ideas now.
Thanks in advance!

What client did you download? I can see/type umlauts on my client (downloaded from Warmane)

I doubt it's something to do with the client and more to do with your Windows regional and language settings. Press start and search for regional, click the first thing that shows up and then play around with Keyboards and Languages (install a language pack maybe?)