Subtitle Language not shown in menu: by design or bug?

I was wondering, why do properly named subs not show up as their language in the subtitle selection menu?
For example I have the following files:

MovieName.2010.mkv (with in it a english language sub)
MovieName.2010.Dutch.srt

Since this follows the guidelines, I expected to be able to select the subtitle by language in the menu or with the remote.
However, I get the following menu items:
- English
- MovieName.2010.Dutch.srt

I also downloaded a sub with the official addon and it is automatically named as:
MovieName.2010.nl.srt

However, even though the renaming was done by the addon, it still also displayed as "MovieName.2010.nl.srt" , instead of "Dutch".

Is this by design? Why have a guideline if it's not used for this?
Is it a bug? Should it work?

(Tested on XBMC 12.2Pre Windows, and Rasbmc 12.1 Raspberry Pi)