What I suggest is to make just structure somewhere at server divided to language sections.
Language section of only 1 language contains subfolders of projects (each with only one .po) and that’s easiest to download for translator. Then can send it by slack to mods, no problem.
Still hold my stand - download original file and create it fully “myself” as translate is the only one proffesional solution for translating.
Translator then can work some ClassicPress installation with this .po and match visible effect at frontend. Those who worked a lot with translations may know what I mean about.
If you are just translate phrase to phrase without project preview, can miss point sometimes.
There are cases translator must shorten translated phrase because of output fieldsize etc.
Also .po file contain phrase createdby and this credit is for translator, not glotpress.
For sure we talk about - one person create one translation- as author. This is most effective method.
Eventually - as many authors, so many unique translation files and then rating can show which translation is the best. Otherwise there’s mess like wikipedia.