At least this has been an headache to me for a long time, especially on Apple TV. When selecting subtitle from the list when playing, I have to scroll to one item, and wait for it to scroll to last position to find out if the extension is the one I want.
Most of time, we name subtitles with same file name as the video file, and with some locale suffix, such as: video_file.enu.ass, so when I selecting subtitle, the useful information will be: [ASS] and [ENU]. So, the idea is, maybe we can put the extension and the locale suffix at begining of the filename, such as [enu.ass]video_filename, something like this.