Hi,
I had the same issue - how to install, as moving it to the german language folder did not work.
I figured out that for one, the name needed to be changed to de-DE.com_jdonation.ini
Second, the language Tags starting with DMS in that file needed to be changed to JD
Voila, it worked,
all the best,
Matthias
herzenssache.org
Ps. maybe I misunderstood and this file was not supposed to be used with JoomDonation but some special version. But anyway, it works with JoomDonation if you do the two things.