Selecting a non-image file type as the alternative image display error.

This can be duplicated in other areas as well when ever the expect image type is not selected.

ERROR: Invalid JSON string
\
Invalid get_string() identifier: 'video/quicktime' or component 'mimetypes'line 5900 of /lib/moodlelib.php: call to debugging()line 6490 of /lib/moodlelib.php: call to core_string_manager->get_string()line 177 of /repository/repository_ajax.php: call to get_string()

{"error":"[[video\/quicktime]] filetype cannot be accepted.","stacktrace":"* line 177 of \/repository\/repository_ajax.php: moodle_exception thrown\n","debuginfo":null,"reproductionlink":"http:\/\/qa2.mroomstest.net\/"}

Steps to Reproduce
Access editor, click insert/edit image.
Select a general image.
Click Advanced tab, enable alternative image
Select non-image for mouse over/mouse out.

Also got one for video/mpeg

Seems like lang/en/mimetypes.php is missing a lot of language entries.