The file to translate

ftp://ftp.billsgames.com/unix/x/tuxpaint/config/po/tuxpaint-config.pot

A link with some help

http://www.tuxpaint.org/help/

And a link with some already translated files in case you prefer to start from another language that you know

http://www.tuxpaint.org/help/po/#tpc and go to the tuxpaint-config section