I tend to avoid locales, and rely on Unicode semantics for regex matching, because it involves less opaque magic, and also recognizes word characters from other languages (which I consider a feature).

As Corion mentioned, you have to find out what encodings your input data and script are in, and decode it before using string operations on it.

See encodings and Unicode in Perl and the Perl Unicode and UTF-8 wikibook for detailed information