Good, was hoping for that answer, as I use mkvtoolnix exclusively and know it works well.
Make sure to analyze the file afterwards. Also keep in mind that Plex tends to be “sticky” on subtitles and audio tracks. Meaning that if you started a file with one track or sub, Plex will make sure that is what is selected when you resume/restart the file, for consistency. If you want to see if the behavior works properly, try a brand new file you haven’t ever played before to see whether Plex does play the first subtitle track as we expect. Or Plex dance the file.
