List the languages needed for programmes, audio, subtitles and the interface separately. A website or app supporting one language does not establish that every programme offers the same language options.
Separate the preferences
One viewer may want English menus and another may prefer a different commentary or subtitle language. These needs can coexist, but they are controlled by different parts of the setup. Write down which are essential and which are simply convenient.
Use real examples during the trial
Try the kinds of viewing each person expects to use and inspect the options actually present. Do not assume a language selector adds tracks that the programme lacks. If a particular option is essential, ask about it before paying rather than relying on a country flag.
Make shared viewing comfortable
Agree on a suitable audio and subtitle combination for the main screen. If people watch separately, include concurrent sessions in the plan allowance. Keep the interface understandable for the person who operates the remote most often, and explain any changes to the household.