Hi !
Following this topic No difference between fr-FR and fr-CA subtitles the issue still is not fixed as of today, a year later.
A lot of my mkv have different subtitles in them, including regular french and canadian french.
The canadian one is, in my opinion, properly labelized.
In MKVtoolnix : Language French(fr;fre) ; Region Canada(ca;124). Those parameter automatically labelized it as French (fr-CA) (+track name “Canadian”, but I doubt Plex will care about this)
However, Plex completely ignore that, and choose instead the lowest french subtitles ID.
It’s weird as there’s both French and Canadian French in Plex subtitles preference.