I have that too.
I've managed to get Tuxpaint in French this way :
1) Downloading latest fr.po on Tuxpaint website *
2) Opening it with poedit and saving it to tuxpaint.mo
3) Copying tuxpaint.mo to /usr/share/locale-langpack/fr/LC_MESSAGES/
4) Giving the appropriate rights (755) to tuxpaint.mo
* not tested but I think it would work fine with fr.mo extracted from 9.21 tar archive
I have that too.
I've managed to get Tuxpaint in French this way :
1) Downloading latest fr.po on Tuxpaint website *
2) Opening it with poedit and saving it to tuxpaint.mo
3) Copying tuxpaint.mo to /usr/share/ locale- langpack/ fr/LC_MESSAGES/
4) Giving the appropriate rights (755) to tuxpaint.mo
* not tested but I think it would work fine with fr.mo extracted from 9.21 tar archive