Right now when you merge an .srt file into an mkv file, the subtitles are set as unknown. How about an option to set to a specific language? Or better yet, read the srt file name and look for ISO 630 standard name i.e. eng for English.
Right now I’ve got MCE running a custom command with mkvprop to add that. When played back in plex this adds a nice touch instead of it saying ‘unknown’ .