Check the edition, not only the movie
Subtitle availability can differ between services and countries. Once you have identified the film, open the chosen viewing edition and inspect its language menu. The original language on an HDPopcorn title page describes the production, not every translated track that might be offered elsewhere.
Subtitles or captions?
Translated subtitles help you follow dialogue in another language. Captions can add speaker information and meaningful sounds. If you need captions for accessibility, check the actual track rather than assuming that any English text option contains the same information. Audio language and text language are separate selections.
Make the text comfortable
Look for supported text-size, background and contrast controls in the player or device. A setting that works on a phone may be too small across a living room. Test a dialogue scene before watching the whole film. For timing problems, check whether the video itself is stuttering, then try the available subtitle tracks or the player's timing adjustment if it has one.
For a dubbed film, use the audio-language guide. If the service offers offline viewing, confirm that the desired subtitles are included in the downloaded edition before disconnecting.