Original language on every title page
Every title page states the original language up front, so you know before you press anything whether you are looking at a Korean drama, a Japanese anime, a Hindi film or a Filipino one, and you can filter any list by original language too. Search works in the original title as well as the English one, which helps when the English title is a translation you would not have guessed.
Subtitles
Press Watch now, open the service, and the subtitle menu in its player, usually a speech-bubble or gear icon, lists every language it carries for your country. Most players let you change subtitle size and put them on a background, which is worth doing on a bright screen.
English dubs, Hindi dubs, Spanish and the rest
The audio menu in the same player lists the dubs. Anime is often available both subtitled and dubbed, Hollywood films frequently carry Hindi, Tamil and Telugu tracks in India, and Spanish audio and subtitles are common across the United States services. Because the tracks vary by service and by country, compare the services Watch now lists and pick the one carrying the track you want. Dual audio, in the sense the download sites used it, is simply that audio menu: every track the service holds, switchable while you watch.
A tip for series
Dubs sometimes arrive a season behind the subtitles. If a later season shows subtitles only, that is the release schedule rather than a fault, and the dub usually follows.
