I just stumbled upon this: https://translations.launchpad.net/josm
JOSM has 9500 untranslated sentences. We should reduce this to zero. I will gradually add some translations, but I cannot complete this alone. Feel free to give a hand.
I wouldn’t waste my time on this.
The number of applications that are not written by Hebrew speaking developers that truly support Hebrew and correct RTL are probably near zero.
Those that do look good are either written by huge companies such as Microsoft or Google or written by Israelis.
Good luck though 
That’s a good point.
I wonder if it’s possible to test JOSM with the already existing translations, to see if things render properly in the first place before diving into this.
It’s open source, so in theory you should be able to download the code and locally compile and run it, but I’m guessing it won’t be easy.