Where can I set the language of mp4 video in MeGUI?

[whiteyes]

Hi.
Is there a place in MeGUI I can set the language of mp4 video?
I only find I can set the language of audio in Muxer.
Everytime I use moviethumbnail or thumbnailme to take screenshots of my media files encoded by MeGUI. They always report undefined to the language of mp4 videos.
http://moviethumbnail.sourceforge.net/
http://www.thumbnailme.com/
It would be great if I can use custom value.

Thanks.

[Lighto]

Use other mp4box GUI such as YAMB or My MP4Box GUI.