But it has as an external service several disadvantages which opposed the philosophy of static websites diametrically.

All Telegram apps are open sourced and the company itself is not for profit, however, their backend is not open source which has raised some eyebrows.

That’s because the Google Translate extension uses some internal Google-only APIs (Mozilla also does the same thing).

Apparently Firefox does have translation built-in, it's just not enabled due to lack of usage agreement / API keys. https://hg.mozilla.org/mozilla-central/rev/a3eb8e502006

Thank you for letting me know about this move by Google. Definitely something to watch. While I agree with Google's position from an end user experience perspective, it unfortunately puts Firefox at a further disadvantage since Mozilla does not have its own language translation initiatives.