They are translatable on Wikidata:

• https://www.wikidata.org/wiki/Special:PrefixIndex?prefix=Queryservice&namespace=8
• https://www.wikidata.org/wiki/Special:PrefixIndex?prefix=Lexicographical-data&namespace=8
• https://www.wikidata.org/wiki/Special:PrefixIndex?prefix=Randomlexeme&namespace=8

I don't know how to submit translations for them, {{edit request}}?
The pure 'zh' locale is work, but the 8 variants of Chinese don't seem to work.

I don't know how to submit translations for them, {{edit request}}?

Yes.

We discussed this in today's bug triage hour and it probably makes sense to at least generate the Lexeme section in the sidebar in the Lexeme extension.

The benefit would be that the messages would be translatable on translatewiki instead of having to create local messages on Wikidata for them and every Wikibase installation that supports Lexemes having to recreate it.

We've discussed it a bit on Telegram. For now, I'll add them to the Wikidata.org extension to make them conveniently localizable into all languages.

However, they can be useful to other Wikibase sites, so it makes sense to put them in a more reusable place some day, for example the Wikibase Lexeme or Wikibase Repo extensions. Sidebar localization is tricky, and sidebars are heavily customized on almost every site. Finding a good way to do it can take some time, so let's put them somewhere now. I'll try to give them key names that are easily reusable so that it will be easy to move them to other extensions if other developers figure out how to do it well.

Change 811216 had a related patch set uploaded (by Amire80; author: Amire80):

[mediawiki/extensions/Wikidata.org@master] Add messages for the sidebar

https://gerrit.wikimedia.org/r/811216

Change 811217 had a related patch set uploaded (by Amire80; author: Amire80):

[translatewiki@master] [Wikidata.org] Add ignored messages

https://gerrit.wikimedia.org/r/811217

Change 811216 merged by jenkins-bot:

[mediawiki/extensions/Wikidata.org@master] Add messages for the sidebar

https://gerrit.wikimedia.org/r/811216

Change 811217 merged by jenkins-bot:

[translatewiki@master] [Wikidata.org] Add ignored messages

https://gerrit.wikimedia.org/r/811217

It's deployed. I made an edit request: https://www.wikidata.org/wiki/MediaWiki_talk:Sidebar#Update_for_good_localization

More or less the same: T273370 (with subtasks T273368 and T273369)

Just doing some house cleaning here. Is this task resolved then? There are no clear acceptance criteria here.

I have checked all messages used in MediaWiki:Sidebar. All of them can now be translated via translatewiki.net, except Recentchanges-lexemes and Villagepump.