The word "destination" has been changed to "destiniation". This is probably a mistake.
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 task 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