It has never been defined what a "word" is in the context of the filetype files. I would have assumed that it meant "identifier" characters, but since the wordchars setting is commented out in all filetypes files, all languages must only use C identifier characters (the default) :)
Even CSS which (correctly) has the dash added to the list is commented out. Its been that way since Enrico added the dash 5 years ago, so nobody seems to be too worried.
So Liviu and Thrawn you are pioneering new territory unless someone wants to define what a "word" actually means. Note also it can't include any Unicode chars >0x100 due to Scintilla limitations so its not possible to make it "right" on newer languages.
Cheers
Lex