in reply to Re^4: Creating new character classes for foreign languages
in thread Creating new character classes for foreign languages

So I'm thinking that it was designed to accompany some additional file, possibly a word lexicon.

Yes, that module is clearly intended to serve only as a wrapper around a separate compiled software library (not written in perl), provided here: http://thaiwordseg.sourceforge.net/.

You have to install that library first (which will probably involve a simple sequence like ./configure; make; make install), and then try installing the perl module, which should include some tests that confirm whether the library was found and turns out to work as intended.