Comment 3 for bug 1101402

I confirm that the gimp package in Ubuntu doesn't ship with *ANY* localisation (it's not only a problem with German translations) while the Debian package has it

as a consequence, in Debian there are several files in /usr/share/locale/fr/LC_MESSAGES :
ls -l /usr/share/locale/fr/LC_MESSAGES/gimp20*
-rw-r--r-- 1 root root 31857 oct. 16 16:00 /usr/share/locale/fr/LC_MESSAGES/gimp20-libgimp.mo
-rw-r--r-- 1 root root 288394 sept. 21 03:28 /usr/share/locale/fr/LC_MESSAGES/gimp20.mo
-rw-r--r-- 1 root root 5915 sept. 21 03:28 /usr/share/locale/fr/LC_MESSAGES/gimp20-python.mo
-rw-r--r-- 1 root root 45770 sept. 21 03:28 /usr/share/locale/fr/LC_MESSAGES/gimp20-script-fu.mo
-rw-r--r-- 1 root root 212059 sept. 21 03:28 /usr/share/locale/fr/LC_MESSAGES/gimp20-std-plug-ins.mo
-rw-r--r-- 1 root root 13902 sept. 21 03:28 /usr/share/locale/fr/LC_MESSAGES/gimp20-tips.mo

and this is not the case in Ubuntu

comparing both packaging (the debian/rules file), in Ubuntu there is a "cleaning" in the common-install-impl:: part (lines 43-49) that seem to delete all the GETTEXT_PACKAGE

conclusion: either Ubuntu should not delete the l10n files, or create some sub-package for each languages
(gimp-l10-de gimp-l10-fr, etc.)