@Lazeez Jiddan (Webmaster)
Not needed.
Since UTF-8 handles all languages, any browser that can properly handle UTF-8 (anything created since 2010) there is no need for special handling of different languages if the text is properly encoded in UTF-8.
I have an old VM with Debian Wheezy and Firefox ESR 52.8 (2016?) which does require the lang properties otherwise is doesn't correctly display a page I have with some kanji characters. That's why I said "some older browsers". In the current versions that is of course not necessary. Logically, even that old version should have displayed the characters correctly but without the lang properties it doesn't.
Could be easily supported if it were ever required, but considering that very few authors would even know how to handle this, it would be superfluous support for something that is extremely rare.
It was a fun remark. I don't see much use for it by authors either, although I do use them in my custom library for clarification of unknown terms or language.
I do think you underestimate a big part of the author population on SOL, I think most would know or learn how to use such a feature very well. The "extremely rare" could become "extremely common" very fast if you think about it: look at the discussions here on the forum about acronyms, military ranks, etc. and you have perfect examples where tooltips can be very helpful.