translation source files

Hi all,

we're going to use phpgroupware at the office (we're a small, no budget 
vzw)Since most of us are dutch speaking I'd like to translate every app 
we're using, perhaps I'll translate others too. (depends on free time 
:-D) I'm wondering, what are the best lang files to start from?
phpgw_en.lang or phpgw_fr.lang

greeting

stijn dumon
aka DuSti