This is the real problem. I really tried to login in Chechen Wikipedia, but there's simply no such page there. Could you please restore all modifications of login-module even if it needed to revert English messages?

If you've unified your account, you should be able to log in at any other language Wikipedia, e.g. [[ru:Special:Userlogin]].

But users without unified accounts cannot log into this wiki at all.

After setting my local test wiki to Chechen language, I am certain this is caused by the slashes in the localised name of the special page.

Maybe this change [1] needs to be reverted.

[1] https://gerrit.wikimedia.org/r/#q,I6e427d047a2f8e58677eb65b50866f767078c255,n,z

I am writing to let everyone know
The site http://translatewiki.net I corrected

http://translatewiki.net/wiki/MediaWiki:Sp-translate-data-SpecialPageAliases/ce

Yeah, exactly because of slashes. But translatewiki do nothing to fix it.

Anyone know how long this has been broken? or if slashes in special page aliases ever worked?

It appears that the special page aliases were added in July, with slashes, and that the version of MediaWiki deployed then (1.22wmf10) also had broken login page.

Anyway, removing the slashes will fix it but new translations are not deployed immediately. They should be deployed sometime in the next 6 hours or so.

Change 97032 had a related patch set uploaded by L10n-bot:
Localisation updates from https://translatewiki.net.

https://gerrit.wikimedia.org/r/97032

Change 97033 had a related patch set uploaded by Siebrand:
Localisation updates from https://translatewiki.net.

https://gerrit.wikimedia.org/r/97033

Change 97034 had a related patch set uploaded by Siebrand:
Localisation updates from https://translatewiki.net.

https://gerrit.wikimedia.org/r/97034

Change 97033 merged by Reedy:
Localisation updates from https://translatewiki.net.

https://gerrit.wikimedia.org/r/97033

Change 97034 merged by Reedy:
Localisation updates from https://translatewiki.net.

https://gerrit.wikimedia.org/r/97034

Change 97032 merged by jenkins-bot:
Localisation updates from https://translatewiki.net.

https://gerrit.wikimedia.org/r/97032

We are in the process of getting the update deployed on Wikimedia wikis, including ce.wikipedia.org. This is why the advise is to translate *what the source code says* and to not start inventing cool adaptations of what translators think will look cool.

Root cause of the issues was this change: https://translatewiki.net/w/i.php?title=MediaWiki:Sp-translate-data-SpecialPageAliases/ce&diff=prev&oldid=4793903

Earned. Thank you very much.