(written from a Production point of view)
Subtitles are on-screen text most commonly used for translation purposes. In Star Trek, subtitles have often been used to translate alien languages into the viewer's language. Subtitles have also been used in DVD and Blu-ray Disc releases.
Examples of in-universe languages which have involved subtitles are:
- Vulcan (Star Trek: The Motion Picture; Star Trek II: The Wrath of Khan; ENT: "Home")
- Klingonese (Star Trek: The Motion Picture; Star Trek III: The Search for Spock; TNG: "Heart of Glory"; Star Trek VI: The Undiscovered Country; Star Trek Into Darkness; DIS: "The Vulcan Hello", "Battle at the Binary Stars", "The Butcher's Knife Cares Not for the Lamb's Cry", "Lethe", "Si Vis Pacem, Para Bellum", "Into the Forest I Go", "Despite Yourself", "The Wolf Inside")
- The language of the Rubber Tree People (VOY: "Tattoo")
- Xindi-Aquatic (ENT: "The Xindi", et al.)
- Xindi-Insectoid (ENT: "The Xindi", et al.)
In many of the larger foreign language areas, such as the locations where the national language is German, French, Spanish or Italian, the dialogue soundtrack of non-native television or movie broadcasts, including the (predominantly) English-language Star Trek, are traditionally replaced with a separately recorded dialogue track with local voice-actors, recorded in the respective language for airing in these regions, a process called "dubbing". Nevertheless, in smaller language areas such as the Netherlands and the Scandinavian countries, it is tradition to maintain the original dialogue track, and have them subtitled in the native language. Dubbing was perpetuated for the older home media format releases such as VHS, but from the LaserDisc onward, the original dialogue tracks have been maintained, with the option embedded to activate the native-language subtitles and/or, in some cases, a dubbed dialogue track.