Delete American English. It's a non-thing anyway. The only thing it does is the date/timestamp stuffs unless you translated things from English to American English but since English is a basic English pack, there shouldn't be anything to translate except regional expressions such as North/South stuffs. Even that's not ever done. Backup the site before deleting stuff. 

Do you have the Locale set to American English perhaps? 

If not, you can check in the language files on the server application/languages but I suggest moving the file out, clearing cache and make sure nothing messed up. If nothing messed up, you can delete the file from whatever folder you had moved it into.