i8n for mnemonics + checksum

The question of whether to support variable seed lengths or not still remains. As of now, it isn't left flexible.
It is hard-coded atm, although word list file size isn't.

I've not done the "50% match check". Instead I do a full check because the words are in files and haven't been populated into a map data structure yet when the wallet restoration is asked for. It really doesn't make a difference as I understood, because we need the entire file parsed any way even for a 50% match check.

Also I've not implemented the "4 letter check if checksum test passes" because it didn't really seem to achieve any substantial improvement in efficiency unless the words are really huge.

Let me know what you think.