Core is complete, so there's no issue there. The issue are the 309 or so open message for extensions used by Wikimedia. Those have not been claimed by Rotem, have they?
No, but there's no certain terminology so I had to translate only obvious strings that need no special interpertation...
As Siebrand said, the core messages are already completed. I don't see any reason for double-effort regarding the core messages.
As for the Wikimedia messages, what is the exact issue? You may translate any message, and ask about the terminology if necessary.
Note that I only "claim" messages that I already update, to avoid double-effort.