Not particularly a coder myself and more of a translator definitely not at home in coding and buidling einvironments like Github, I'd like to suggest that the translation work on the resources properties files be moved off site to one of the online localisation platforms like Crowdin, Transifex, Weblate...

Benefits:

• Translators can focus on the strings to be translated
• Translators need not worry about possibly breaking the code syntax (or inadvertently adding an empty line ;-)
• Translators will receive notifications when source files are updated
• Translators get a clear indication of the number/percentage of strings untranslated/modified/approved
• If a strings is (subtly) changed, the online translation platform will simply mark the item changed and put it on the to do list
• A glossary will help maintaining consistency throughout the entire translation
• Project manager(s) can pull in all translations at any time, be it daily or only just before a release
• ...

The Inkscape project recently made the move from translations in source code files to the weblate online platform.
I believe that all online localisation platforms I mentioned above provide free plans for FOSS projects.