[FFmpeg-user] Set chapter languages in mkv format

[Da Rock]

I've nearly got a perfect setup to encode my videos that I have. I have 
the matroska format and metadata tags all set for languages,titles and 
such for each track. I also have finally sorted out chapters... but:

When I input my ffmetadata file, I then go to mkvinfo and check my work; 
what I find is that under the chapter display it shows the chapterstring 
(as it terms it - title in other words), but under language it says und 
(undetermined).

Pedantic as it may sound, it does bug me a bit. How do I change it?

The chapter stream is 0 (first input), and I've tried setting 
chapterlanguage in the ffmetdata file, -metadata:s:m[:0] (both 
iterations that is), -metadata:m, -metadata:i:0 all to no effect. What 
is the method for this madness?

My ffmpeg is version 2.3.6.

Cheers