Hi Jer,
Thanks for the comment.

It seems that patterns are translatable with Polylang PRO. I’m not sure if an update happened along the way, but now I get the option to translate patterns as well. This is a big plus, because you don’t need to rely on template parts.

Not being able to reset the part after translation feels very frustrating, but I guess it’s inevitable, a side-effect of the overall fragility of “template” content in FSE. Once you start editing, you can never “update” a section with fresh templates in the theme files.
Yeah, this is a bit of down side. Maybe there is a better option, but at the moment I couldn’t see any work around for it.

So far the project works pretty smooth, I’ll make an update once more content is being added.
An important part for me was also translating the custom Gutenberg blocks that this project has.
https://devmaverick.com/how-to-translate-a-custom-wordpress-gutenberg-block/

Interesting that “parts” can be translated but not “patterns”. It implies a specific workflow while preparing themes before deployment. Not being able to reset the part after translation feels very frustrating, but I guess it’s inevitable, a side-effect of the overall fragility of “template” content in FSE. Once you start editing, you can never “update” a section with fresh templates in the theme files.

If you feel like it, please share any updates on the project you described here, I’d be interesting to know the long-term experience 🙂 (and if your site doesn’t email replies, feel free to email me a link to your reponse!)