If I’m doing it all myself (or managing translations via chat or Discord or something), then I just need TranslateKit.
If I want to crowd-source the translations, and/or allow folks to do it themselves in their own time on a separate system, I could consider setting up Crowdin.
Might start with just TranslateKit for now.
More wisdom from Cihat:
There are also a bunch of alternatives - Phrase, Lokalise, Transifex, POEditor, CrowdIn.
All have different pricing and different focus. The general term is “translation management system”.