Ah, this comes from ext-livetranslate...

Similar requests should go to this page (according to a message shown when trying to edit the source)

I note that, while https://translatewiki.net/wiki/MediaWiki:Apihelp-livetranslate-description/en shows the correct spelling, that correct spelling is not reflected in the actual message in the code. It was apparently edited on translatewiki in March 2016, but changes to 'en' messages are not copied from translatewiki because English is the source language.

Fixing the message itself needs a patch in Gerrit to that en.json file. It's pretty good first bug to do so. Someone might also want to start a discussion on translatewiki about cleaning up 'en' messages that have been edited like that one was.

I reported the issue on https://translatewiki.net/wiki/Thread:Support/Fix_spelling_in_the_source_page
@Anomie Maybe we should also start a new task for this wider issue and close this one

Well, this one may as well stay open until someone fixes apihelp-livetranslate-summary and apihelp-livetranslate-description in en.json.

@Anomie Yeah, sure, the new one should be parent of this

Change 361215 had a related patch set uploaded (by Umherirrender; owner: Umherirrender):
[mediawiki/extensions/LiveTranslate@master] Fix typo in word 'destination'

https://gerrit.wikimedia.org/r/361215

Change 361215 merged by jenkins-bot:
[mediawiki/extensions/LiveTranslate@master] Fix typo in word 'destination'

https://gerrit.wikimedia.org/r/361215