There are also reports of people getting a "server error" when trying to request translator rights, dunno if it's related but needs investigation.

Trying to get more info from https://translatewiki.net/wiki/User:Guntijs

(In reply to comment #1)

There are also reports of people getting a "server error" when trying to
request translator rights, dunno if it's related but needs investigation.

Trying to get more info from https://translatewiki.net/wiki/User:Guntijs

It isn't. Bug 38939.

Now if I try to create a thread to request rights in as I get a fatal:

Database query syntaxত ত্ৰুটি হৈছে। ছফ্টৱেৰত থকা কোনো বাগৰ বাবে এনে হব পাৰে। অন্তিমবাৰ চেষ্টা কৰা ডাটাবেচ কুৱেৰীটো আছিল এনেধৰণৰ:
(নিহিত SQL query)
"Thread::insert" ফাংচনৰ পৰা। ডাটাবেচে প্ৰেৰণ কৰা ত্ৰুটি: "1062: Duplicate entry '2634092' for key 'thread_root' (localhost)"।

I managed to delete one if the two existing threads, although with the error below; however even https://translatewiki.net/w/i.php?oldid=4039471&action=delete fails saying that someone may have already deleted the thread, I managed to delete only its child.
So from FirstSteps I still get:

A database query syntax error has occurred. This may indicate a bug in the software. The last attempted database query was:
(SQL query hidden)
from within function "Thread::insert". Database returned error "1062: Duplicate entry '2387954' for key 'thread_root' (localhost)".

Post 22042 has contaminated reply 22854. Expected 22042, got 22040

Backtrace:

#0 /www/translatewiki.net/w/extensions/LiquidThreads/classes/Thread.php(989): Thread->checkReplies(Array)
#1 /www/translatewiki.net/w/extensions/LiquidThreads/classes/DeletionController.php(45): Thread->replies()
#2 /www/translatewiki.net/w/extensions/LiquidThreads/classes/DeletionController.php(48): LqtDeletionController::recursivelyDeleteReplies(Object(Thread), 'Thread padre ca...')
#3 /www/translatewiki.net/w/extensions/LiquidThreads/classes/DeletionController.php(27): LqtDeletionController::recursivelyDeleteReplies(Object(Thread), 'Thread padre ca...')
#4 [internal function]: LqtDeletionController::onArticleDeleteComplete(Object(WikiPage), Object(User), 'test: [[bugzill...', 2634092, Object(WikitextContent), Object(ManualLogEntry))
#5 /www/translatewiki.net/w/includes/Hooks.php(255): call_user_func_array('LqtDeletionCont...', Array)
#6 /www/translatewiki.net/w/includes/GlobalFunctions.php(3871): Hooks::run('ArticleDeleteCo...', Array)
#7 /www/translatewiki.net/w/includes/WikiPage.php(2608): wfRunHooks('ArticleDeleteCo...', Array)
#8 /www/translatewiki.net/w/includes/Article.php(1629): WikiPage->doDeleteArticleReal('test: [[bugzill...', false, 0, true, '')
#9 /www/translatewiki.net/w/includes/Article.php(1466): Article->doDelete('test: [[bugzill...', false)
#10 /www/translatewiki.net/w/includes/actions/DeleteAction.php(38): Article->delete()
#11 /www/translatewiki.net/w/includes/Wiki.php(439): DeleteAction->show()
#12 /www/translatewiki.net/w/includes/Wiki.php(305): MediaWiki->performAction(Object(Article), Object(Title))
#13 /www/translatewiki.net/w/includes/Wiki.php(565): MediaWiki->performRequest()
#14 /www/translatewiki.net/w/includes/Wiki.php(458): MediaWiki->main()
#15 /www/translatewiki.net/w/index.php(59): MediaWiki->run()
#16 {main}

(In reply to comment #3)

Now if I try to create a thread to request rights in as I get a fatal:

To clarify, this is only about FirstSteps (as the rest of the report); creating a new thread with summary "{{LanguageHeader|as}}" works, but now I can't delete that one either at https://translatewiki.net/w/i.php?oldid=4579708&action=delete

Can you please try to get steps to reproduce for this? I'm not sure if this is fixable without...

The steps have already been provided, but I can try to make them clearer.

Steps for FirstSteps bug:

1. Log in as new user or other account without translator status
2. Request to get translator rights in "as" language

Steps for LQT side of the bug:

1. Go to Project:Translator
2. Try and create a thread with "{{LanguageHeader|as}}" as summary
3. Observe the lottery of random weird results, including

3a) failure at creating the thread
3b) failure at replying at it
3c) success at replying at it, but failure at replying to the reply without overwriting it
3d) failure of deletion of the thread

I'll try to fix this, probably by fixing the corrupted database state by hand.

Worked around in https://gerrit.wikimedia.org/r/57501