Max Nelson in The Point:
The subtitles that appear under most foreign-language films in British and American movie theaters tend not to call attention to themselves. Moviegoers only notice them when something goes wrong—when they’ve been rendered bulbously large, or when they’ve been colored a sickly yellow, or when they disappear against a white object, fall out of sync with the dialogue, flit abruptly to another region of the screen or bear the goofily garbled translations of which a Google search for “bad subtitles” gives you hundreds of examples. Possibly because they’re designed to go unremarked, subtitle translations remain one of the least studied and most overlooked features a film can have.
The average English subtitle is a modestly sized, pleasant-looking bar of thin sans serif text between 32 and forty characters long. Unlike its ancestor, the silent film intertitle, which was often bedecked with illustrations suited to the movie and sometimes included fonts and effects that matched the words it showed, the subtitle can’t be incorporated into a film’s overall design. In that event, it would become part of the film; it, too, would need to be subtitled when the film was screened for other markets. As a visual element, the subtitle is extraneous, replaceable and unassimilated into everything else in a given frame. Critics of subtitles have protested that they seem stuck onto films where space wasn’t made for them, as if they need to atone for defacing the movie by doing their business as quietly and modestly and unobtrusively as possible.