I use a browser plugin to help with this; so that I get asked if the page should be translated, which of course, makes it much easier to read:

Change 459625 had a related patch set uploaded (by EBernhardson; owner: EBernhardson):
[mediawiki/core@master] Render advanced search in interface language

https://gerrit.wikimedia.org/r/459625

There are more places where the namespace names in content language are shown in the UI:

• Special:ListGroupRights, See https://mr.wiktionary.org/wiki/Special:ListGroupRights?uselang=en#Namespace_restrictions
• Special:WhatLinksHere, See https://mr.wiktionary.org/wiki/Special:WhatLinksHere?uselang=en
• Special:RecentChanges, See https://mr.wiktionary.org/wiki/Special:RecentChanges?uselang=en
• Special:Watchlist, See https://mr.wiktionary.org/wiki/Special:Watchlist?uselang=en
• Special:Import, See https://mr.wiktionary.org/wiki/Special:Import?uselang=en
• Special:Contributions, See https://mr.wiktionary.org/wiki/Special:Contributions?uselang=en

A change of the language of the namespace names from content language to user interface language should be consistent at all places.

I disagree this should be the same in every place. I think it really depends on the use case. Reporting to a user a list of some thing that exists, like an existing page title or namespaces groups have rights to, might make sense to be in the content language of the wiki. Asking a user to choose items from a list they can't read seems a distinct issue.

I'm perfectly willing to delegate the choice to Language-Team though.

https://mr.wiktionary.org/wiki/Special:Contributions?uselang=en shows the namespace names in a drop-down list.
https://mr.wiktionary.org/wiki/Special:Search?profile=advanced&uselang=en shows the namespace names in a checkbox list.
I think this is no difference and the language of the namespace names should be consistent at all places of the UI.

@Amire80 any thoughts?

Hmm... There are several considerations here.

I agree about Special:Search—it should be in the user language. It can possibly also be used when moving pages, and in the other places that @Fomafix suggests.

Some care is needed for other places, though. The original English names work everywhere for links, so if the user language happens to be English, as I guess it is for @Whatamidoing-WMF and @EBernhardson, then [[User:अभय नातू]] will work as a link in mr.wikipedia. But if the user language is Russian, for example, then it will only work in Russian (and maybe a few other wikis that have Russian as fallback, and I'm not even sure about that). So for page titles that may be used as links it's probably better to use the wiki's language, or to explicitly use English.

Also, there are namespace names that are local only to particular wikis and are not translated. "Portal", for example, is local only to a few wikis, and AFAIK is not centrally translatable. Neither is the "Txiki" space in eu.wikipedia. I guess that there's just nothing that can be done about them.

@Nikerabbit , any more thoughts on this?

The merged patch only changed the "old" UI for Special:RecentChanges and Special:Watchlist, the new rcfilters UI is not affected by this change and perhaps should. (I failed to find from where the list of namespace is populated in rcfilters).

Change 459625 merged by jenkins-bot:
[mediawiki/core@master] Render namespace lists in the user's language

https://gerrit.wikimedia.org/r/459625

There are more places where the namespace names in content language are shown in the UI which are not covered by rMW9f28aa0709d0:

• https://mr.wiktionary.org/wiki/Special:AllPages?namespace=2&uselang=en (Here is also an inconsistency between the namespace selection list (content language) and the namespace name in the caption (user interface language).)
• https://mr.wiktionary.org/wiki/Special:Listgrouprights?uselang=en#Namespace_restrictions