Another one, though I’m not sure if this is what you’re thinking of, is temporary subtitles for a very short section of the film where it’s important for the viewers to understand what’s being said, but not some of the characters. For example, just now I was watching ‘Toy Soldiers’ and a boy claimed not to speak Spanish. The villain then said ‘put a bullet in him’ in Spanish, subtitled in English, and the boy said ‘no, wait!’ showing that he did speak Spanish after all.
You also often see it used for comic effect, when either what the character’s actually saying in the foreign language is different to what the translator’s claiming, or us being able to understand the foreign-language speaker more than some of the characters puts a completely new spin on things.
One example of this is in Arrested Development, where the little Korean boy says ‘An nyoung’ subtitled as ‘hello,’ but everyone around him thinks he’s repeatedly saying his own name.
This is somewhat different to what you were asking, since these subtitles are usually embedded rather than available on a subtitle track. And man, that was a long, rambling post - apologies.