A volunteer reported this issue and I was able to repro:
- Go to https://www.mediawiki.org/wiki/Developer_access.
- Click "Sign up for developer access".
- Fill out all fields. I used the username "testaccount".
- Submit and an account is created but the following error is shown at https://wikitech.wikimedia.org/w/index.php?title=Special:UserLogin&action=submitlogin&type=signup:
MediaWiki internal error. Exception caught inside exception handler. Set $wgShowExceptionDetails = true; at the bottom of LocalSettings.php to show detailed debugging information.