Three different language questions
A production's original language, a dubbed audio track and a subtitle track describe different things. SFlixTV's filter uses the recorded original language to organize titles. The player you choose supplies the available audio and text tracks for that offer and country.
Make text comfortable to read
Open the player's language or accessibility menu. Where customization is supported, try a larger size, outline or background panel before starting a long episode. A style that works on a tablet may be too small across a room. Captions can include relevant sounds as well as speech, which may make them more useful than dialogue-only subtitles.
If the timing seems wrong
Check that the title, episode and edition match. Then reselect the track or reopen the same chapter using the service's normal controls. An alternate cut or recap can produce a mismatch that changing font size cannot solve. If one track fails while another works, that is different from the whole video being out of sync.
For a group, choose the shared language before pressing play. It is easier to settle the track at the start than interrupt a key scene later. Browse original languages for a new production, or use playback help when the problem is broader than subtitles.