To get your voice into it, you would have to edit and replace every one of the 7000 voice lines, and even then the lip sync would be wrong. So, in my opinion, not worth it ;). I recommend only changing the subtitles.
(And, when you are done, email it to me, and I'll upload it to The D.O.D. (
http://dod.dotagame.com). I can add a language pack sention to the site :). If anyone has any they've done already, send them in)