You might want to have a look at Xapian (and its associated front-end, Omega).

It's C++, admittedly, but the source is available and there are Perl bindings. We use it at work, and it's quite happy indexing utf-8 documents (including Japanese). There are also various language stemmers available - no Serbian at present, sadly - I can't comment on how good they are, as we don't use them.

If nothing else, it may give you insight / inspiration for your own efforts.