I shared the answer here:
I've seen this on some MKV files lately. But not all. I don't believe it is a function of MC, but of how the MKV file is tagged. For example, if the file was marked as German, even though it was English, and had English Subtitles, then MC would show the Subtitles as it is supposed to.
As I noted last year (
), I've seen it in some MKV files lately. The "problem" is with the files themselves. It wasn't exactly what I described, but the same issue: The Language of the included Audio is not tagged in the file.
You see, MC needs to know what language the Default or selected audio track is, in order to determine if it matches the available Subtitles tracks. How would MC know that? Only if both the Subtitle and Audio tracks are tagged with the language of course.
I found four MKV files that have Subtitles in them. Most I see don't. Of the four, three played English Subtitles even though my PC language is English, my Default Subtitle language is English, and my Default Audio Language is English. For each of those three I had to turn off Subtitles when I had watched them, as shown by the contents of the [Playback Info] field, which included the setting "(9:Subtitles)(4:None)". All three of these problem files had the Subtitle track tagged as English, but did not have the Audio track tagged with any language. When MC doesn't know what language the Audio track is, it takes the conservative approach and shows the Subtitles. Basically, <Unknown Language> does not equal <Default Language>.
The one MKV file that had a Subtitle track in it, but didn't automatically show the Subtitles, had the Audio and Subtitle tracks tagged as English.
I checked what was in the MKV files using
MediaInfo, which showed the tags mentioned above as "Language : English" in each tag section, if present. If you are seeing English (or your default language) Subtitles being displayed on a video for which you are playing an English (or your default language) audio track, check the tagging in the file.
Note: The language tag in MC is not the same as the Audio and Subtitles track language tags, of which there can be multiple in one file. Also, the MC [Language] tag isn't written to files by default, and if that capability is turned on, the tag is written to the Sidecar file in the case of MKV files. It probably could be written to the MKV file in the Video portion of the tags. But that is a different issue.
TL;DR Bottom line: MC Subtitle functionality is working correctly.