I don't know if this maybe should be somewhere else, but anyway. I resorted to using Windows in the end, and then it was no problem.
I initially struggled because I thought I needed to preserve file dates in the zip archive, based on comments I were reading. But I failed to get the files backdates in the archive. In desperation I just tried with a created zip file with current dates on my edited files, and it worked fine.
I played with both WinRAR 3.92 and the most recent one, and both works just fine. And my archive do have a current timestamp on the files when looking inside the zip file. But my system didn't care.
Adding with zip under Unix systems constantly failed, and when inspecting, the files got various Unix attributes and information added, which I suspect might be what upset my nav system. Basically, just keeping it all very Windows-centric made it all work just fine.
I can report that I fixed various translations, both in text and TTS, in Swedish. And now my system don't hang when it comes to give warnings. Seems the TTS system is a bit fragile in that if a translation for a phrase is missing, the TTS system for that group of messages hangs, and no more messages at all comes through.
For me, what happened was that the translation for "Reduce your speed." was missing. Once it wanted to say that phrase, all warning messages stopped working. So no more overspeed audio warnings, no more speedcamera warnings... But turn directions still worked with audio.
Not sure if this is a known thing, but now it's in here, for any future people passing by.
Also, in case someone stumbles on another small detail, the dictionary files are UTF-16 little endian files. Hopefully most people are using tools that already understands this, but just in case. Another small piece of information someone might find useful.