I'll let the others fill you in on the translation side, but I maintain the Holidays library in kdepim and would welcome a contribution for Bosnian holidays. Basically all I need is a list of all the official public holidays and the main unofficial ones, the rules for what dates they fall on and if they change under certain circumstances, the Bosnian names and informal English translations, and a reference website (usually some official government site). Wikipedia is always a good place to start and it has a list at
http://en.wikipedia.org/wiki/Public_holidays_in_Bosnia_and_Herzegovina and I'm in no position to know how accurate that page is.
John.