I recently saw ISteamApps Interface (Steamworks Documentation) “This falls back to the Steam UI language if the user hasn’t explicitly picked a language for the title.” There’s also ISteamUtils Interface (Steamworks Documentation). I don’t know when they added these, but I’m pretty sure they’re older than the Steam dll that ships with UDK.
What I did was copy the up-to-date Steamworks SDK into my game’s source code, compiled, fixed errors, compiled, fixed errors, compiled, and fixed errors until it worked. I think there are a couple of functions that just aren’t there any more, and there are a bunch that now return qwords instead of dword ints. It wasn’t too bad for me because my game is entirely single-player and I didn’t really care about any of the netcode. It might be more complicated for you.