The initial discussion in the Incubator wiki mostly supports this idea:
https://incubator.wikimedia.org/w/index.php?title=Incubator:Community_Portal&oldid=4370387#A_proposal_for_a_big_reform_of_the_Incubator

Any news?

In T189982#4500647, @Legoktm wrote:

Just to note, that editing the Gruntfile.js should not be necessary at all. Extensions should have their Gruntfile.js set to read the canonical list straight from extension.json (e.g. https://gerrit.wikimedia.org/g/mediawiki/extensions/AddPersonalUrls/+/master/Gruntfile.js#5), so it only needs to be updated in one place. If they aren't already doing this, this would be a good opportunity to migrate them.

Here's the current situation in CX2 production, translating from English into Hebrew.

It's not fully resolved.

Niharika asked for my comment on this.

In T189982#4500589, @Legoktm wrote:

Should we have a script to do this?

Still happens in CX2, most likely related to the domain renaming.

I tested it further, and found that the issue is in Yandex.Translate and not in CX.

Yes, still happens in CX2.

Cannot reproduce in CX2. Tried in Achilles tendon rupture and several others.

In T190047#4496883, @Nemo_bis wrote:

The "legacy" extensions could just be removed from the group without creating another one.

I didn't examine the relevant Cite and VE code, but it probably must not be translated, because it may be processed as actual JS or JSON code.

It's probably an easy thing to do. It will be somewhere around here: https://phabricator.wikimedia.org/diffusion/ECTX/browse/master/api/ApiContentTranslationPublish.php$175

Yes, can be reproduced.

In T152140#4408482, @Pginer-WMF wrote:

@Amire80, can you confirm whether this happens in version 2 of Content Translation?

In T96147#4281694, @Shizhao wrote:

Integration TOTW to list? https://meta.wikimedia.org/wiki/Translation_of_the_week

(This discussion of language codes is not really related to the topic of this task. There are better places to have it. Thank for understanding.)

Deployed. Thanks to everybody who helped.

@Verdy_p, your proposal sounds far more complicated. Adding URL rewrite rules and a lot of namespaces will make things very different from how usual wikis work. One of the central points of the proposal is making it easy work with Wikidata and Content Translation, both of which assume that there is one language per wiki. Creating a new wiki shouldn't really be complicated. It's just a matter of automating the current wiki creation procedure, and @Urbanecm says that it's doable.

Thanks for creating the task.

Thanks, @tstarling!