(written from a Production point of view)
Subtitles are on-screen text most commonly used for translation purposes, but also frequently for text commentaries. 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, on several occasions also – but not always – for the audio commentaries when included.
Examples of in-universe languages which have involved subtitles are:
- Vulcan (Star Trek: The Motion Picture; Star Trek II: The Wrath of Khan; Star Trek III: The Search for Spock; ENT: "Home")
- Klingonese (Star Trek: The Motion Picture; Star Trek III: The Search for Spock; TNG: "Heart of Glory"; Star Trek V: The Final Frontier; 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")
- Denobulan (ENT: "Dear Doctor")
- Xindi-Aquatic (ENT: "The Xindi", et al.)
- Xindi-Insectoid (ENT: "The Xindi", et al.)
- Romulan (PIC: "Remembrance", "Maps and Legends", "The End is the Beginning")
There was some deliberation over whether a line of Russian that Chekov speaks in Star Trek III: The Search for Spock would be accompanied by a subtitle, though it ultimately wasn't. (Starlog, issue 91, p. 40)
Non-production use of subtitles
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 film 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 Dutch-speaking Europe, the Scandinavian countries and Portugal (though not Brasil where dubbing is commonplace), it is tradition to maintain the original dialogue track, and have them subtitled in the native language – even though dubbing is utilized for television programas aimed at the very young. Dubbing was perpetuated for the older home video format releases such as VHS, but from the LaserDisc optical disc format onward, the original dialogue tracks have been retained, with the option embedded to activate the native-language subtitles and/or, in the above-mentioned cases, a dubbed dialogue track.
English-language optical disc home video format releases usually contain at the very least an English-language subtitle option for the deaf and hard-of-hearing (SDH) as well.