We need to set priorities. Having an updated language file for all our supported translations is certainly not one on my list… It should also be much easier to create a minor release 5.9.1 with only updated translations and maybe some critical bugfixes.
I think this script actually already exists RawTherapee/tools/generateTranslationDiffs at dev · Beep6581/RawTherapee · GitHub
I think this is not necessary at the moment: quite some active members on this forum have been using the latest dev builds for some time now. Some reports have been filed, but no critical bugs have been found. I would be willing to put 5.9 out there as a culmination of a rough two years, accept that it will not be perfect yet, but then work towards a stable future.