Subtitles are simply translations of speech or text into another language, and are generally (though not always) center aligned near the bottom of the frame.
This is wrong. Subtitles and closed captions serve the same purpose and the terms are largely interchangeable. It's an Americanism to associate subtitles specifically with translations or closed captions specifically with EIA-608.
The essential function of subtitles and closed captions is to enable a viewer to read dialogue (or contextual audio elements) without needing to either hear or understand the audio. It may be in the same language or not.
As one example, in some Chinese markets TV and movies are all subtitled in Chinese, not (primarily) for the deaf, but because the standard Chinese subtitles are intelligible to readers whose only spoken language is a mutually unintelligible dialect.
Sorry, but this is wrong. Closed captions may include non-speech audio as text for hearing impaired which subtitles will assume just speech translation not things like "[wind noise]".
The essential function of subtitles and closed captions is to enable a viewer to read dialogue (or contextual audio elements) without needing to either hear or understand the audio. It may be in the same language or not.
As one example, in some Chinese markets TV and movies are all subtitled in Chinese, not (primarily) for the deaf, but because the standard Chinese subtitles are intelligible to readers whose only spoken language is a mutually unintelligible dialect.