You need to get the term “forced” out of your head. Translate “forced” to “subtitles for foreign parts and translations of text on screen”.
If you have a movie with a full audio track in a foreign language, you want a “full” subtitle track. Hence why the track without the “forced” flag is chosen, because it is assumed that a subtitle track without the “forced” flag is a regular, full subtitle track which writes out every bit of dialog (and additionally translates foreign language text on screen).
A track with the “forced” flag activated is always a track which contains translations if parts of the audio track are foreign. Or if there is text on screen in a foreign language.
Never set the forced flag on a “full”/“complete” subtitle track. It isn’t appropriate.
Always keep in mind that every user of your server can have it’s own, individual language preferences. If one of them needs a “full” subtitle track, because of bad hearing, he will set his language preferences to “subtitles always activated”. Which will pick the “full” subtitles over the “forced” ones.
But if the track with the full subtitles is mis-tagged as a forced one, the automatic track selection won’t work for this user.
