Just comment a mistake in support topic on phpBB Spain,
Seems a bug of version phpBB 3.1 and phpBB 3.2
When you make a group of new extensions and try to find a language, and can not find it because it does not check before if there is an input language for this group.
It appears that the error can be on /includes/acp/acp_attachments.php file (line 1231).
Screenshots in Spanish, sorry.
Reported in phpBB Spain: http://www.phpbb-es.com/foro/viewtopic.php?f=149&t=41210