API change in Language object casting - language codes.

Hello! I'd like to help developing OpenClassic but I'm quite a beginner in programming so I only added the additional language support with shortened language codes (like English -> US). Newly-written module allows the user to paste the language file in .minecraft_classic\lang dir which is automatically created. User has to also create the .id file of language which should consist of language name and language code. I also give a link to my translation in Polish: https://www.dropbox.com/s/ecml2nq1qd8eknh/polish.zip . That's part 1 of 2 of this modification.