Translate the website

Perhaps the site should be translated in order to implement the system now to manage translations?

Translating the UI (the site) would be a good improvement.

Maybe setting up something on (which is free for FOSS projects) to have community contributions?

First step would be to extract the strings from the JS/HTML into .po files and integrate a JS library such as Vue I18n (for example, maybe there are better ones)

Or maybe we can just translate the strings directly from the Flask/Python side (since we’re serving an html template). Something like Internationalization — Python 3.10.0 documentation could work then. We still need to extract the proper strings into .po automatically though.

Effectively weblate looks interesting.

Using a vue library seems the best thing to do as there is text in the javascript, however I don’t know what impact this has on SEO.

Since many parts are already rendered in vue, I don’t think it will affect SEO.

Okay, but ideally all texts, title and meta html should also be translated.

Yep; it should be doable by using Python’s template variables.