The selected track may contain forced translations or signs rather than subtitles for the complete programme.
Why this happens
A short translation when characters change language is not necessarily a broken full-dialogue subtitle. Some tracks are designed to show only selected speech, signs or other information the main audience would otherwise miss. They can remain quiet through most of a programme and appear only where needed. A player may identify these with a forced flag or a related label, although the wording is not identical in every application. The track’s purpose is therefore as important as its language name.
Inspect the available subtitle choices on the item that is playing. If a fuller track exists, compare it with the one producing occasional lines. Kodi’s language documentation distinguishes forced subtitle behavior from other language preferences, which illustrates why a single language setting does not describe every subtitle choice. Do not assume a track is complete merely because its label matches the soundtrack language. If no full-dialogue option appears, a font or timing adjustment cannot generate dialogue that is absent from the track. Keep the track label with the result.
A useful way to work through it
Read any forced, foreign-parts or similar label beside the subtitle language.
Compare another available track during an ordinary dialogue scene.
Treat an absent complete track as a source/track question rather than a font problem.