There doesn’t seem to be much activity around Juris-M lately, it hasn’t been updated since 5.0.93 (Zotero is now on 5.0.96) and for the last few days downloading or updating the app has not been possible, not sure why.

Personally I also don’t really understand why Juris-M isn’t just integrated into Zotero.

There are essentially three ways in which Juris-m diverges from Zotero:
1. It has improved legal support with not just additional item types but also things like modular elements in styles that behave differently depending on jurisdiction, parallel citations as used in anglosaxon legal writing, etc. Zotero has made pretty clear that they don't think they have the right expertise to implement the full complexity of international legal citation, so that's just not going to happen.
2. The original "Multilingual" part of Juris m, which allows the addition of translations and transliterations of titles and names to items. I don't think there's currently a statement from the Zotero devs about this, but while it's very useful, it's also quite messy GUI-wise, it's not at all rooted in the current data model, etc., so this would be an absolutely massive undertaking for a relatively small group of users: contrary to what some of you are implying, these aren't people working in non-English, non-Western, or multiple languages, but it's people who work in traditions that include a lot of going back and forth between translation/transliteration/original titles, a much smaller subset of the above groups.
3. Juris-m uses its own version of CSL and the developer writes the citation processor himself, so he can make changes to CSL more quickly than Zotero which, like 30+ different tools using at least 5 different citation processors uses standard CSL. This means some of the more lightweight changes that have existed in Juris-m will definitely make it to Zotero. The ability to sort bibliographies by language as mentioned by the OP (which is already possible in Zotero using unofficial/nonvalidating styles btw., there are a number of existing threads here with directions) is one of those things, as is the inclusion of some additional legal item types (treaty e.g. will likely be in the next major version of Zotero) and very likely some lightweight additional support for multilingual writing such as the ability to include translated titles, but that one is further out.

PubMed metadata provides non-English language article titles with an English-language title within square brackets. It also provides the title in the original language. At my university several faculty insist on both the original-language title and the English translation be included in a citation.

Is it likely that the new CSL and Zotero's implementation will eventually facilitate this 2-title business? The original language is provided with the nbib export.

Thank you all for your comments here!
I agree that Juris-M is overkill for most of users, but the official support for the ability of displaying bibliographies depending on language is really essential.

@adamsmith : I am sorry if I overlooked this in the search results, but as far as I know, while sorting by language can be done easily by adding

"<"key variable="language""/>" (I know it is wrong code, but not sure why it is hidden without adding ")

there is more complex requirement in the displaying of authors' names and sorting by Last name vs First name depending on the language groups (like one in my example). Can it be done by editing CSL file?

Yes, that is what I did till now as a workaround (my case is Vietnamese). In my example, I didn't mention other things related to language, that is:

Vietnamese:
1. Family name - Given name (in full, without initials, i.e. Nguyen Quang Hung)
2....

English
3. Given name in initials form - Family name (i.e. J. Doe)

Could you please tell me how to do that?

Juris-M is still being actively developed (though the download links are currently down). The latest production version is 5.0.93, but the beta is 5.0.96.
Name sorting is an ultimately intractable problem because different authors prefer different orders, especially people with East Asian names publishing in non-Asian languages, but generally Juris-M gets it right.

enclose word "code" in angle brackets to open and close with a closing tag containing the word code.

<code> 1234 </code and end the close code with a greater than angle bracket

I am afraid that this is not possible. I think you can only set the "et al" language for all the citations within a specific Word document. In "Set document preferences" from the Jurism Word processor plugin, you can choose "Russian" or "English" etc. in the language drop-down field below the style list.
Regarding the Jurism-specific multilingual options, see: https://juris-m.github.io/posts/2020-11-08-0.html