I do not know details of the others, they may be coming from core files. But I can comment on #2
Subscribe button and everything else that comes after clicking that button come from the Member Portal component. The repo is very helpful, explaining how to do this clearly.
- You can check out that repo, translate every text locally, build it/generate a new portal.min.js, upload to your server and change your config.production.json file to point to the new portal.min.js
- (Sorry for the shameless plug) Use my service. If you decide to go this route, please let me know if you have any questions. I’d be happy to help out.