I just did a quick search on this and found this blog past which may be helpful. Apparently some of the culture names used by MS were not compliant with RFC 4646 so they were renamed in some service pack or update to bring them into compliance.
So try using sr-Cyrl-BA
However, be aware that if you set the default culture to something other than en-US, its up to you to make sure all the resource files are not missing any keys. If there are any missing keys in the default resource files it can throw null reference exceptions when it tries to use the missing key.
If you make a translation please contribute it to the project. If you make a .zip file with the translations and send them to me at joe dot audette at g mail dot com I will include them for you.