For subtitles to be effective, enjoyable and acceptable, a linguist must take into consideration the following aspects:
What is the specific area of translation – are we using the appropriate and relevant terms for the specific topic in the target language, as are being used for the same topic in the source language?
Is the style of speaking formal, informal, colloquial or otherwise in the source language? Is it romantic, narrative, respectful or otherwise? Is the same style of speaking being employed in the target language?
Is it a film or advertisement? Language usage has to be appropriate to the nature of the media.
Cultural and Colloquial Cues:
Is the style and content of the speech appropriate when said in the target culture? If not, how can the same message be communicated in a culturally appropriate way? Is the kind of slang that is used in the source culture and language, acceptable in the target? Does it need to be adapted?
Is the translation too literal? Do we translate the words one by one, or do we translate the overall function of the words? For example, when a person says, “good night”, we know he is taking leave. We should not translate only the words “good” and “night” but find out how people take leave in the target culture. We may want to translate it as “see you again” or “greetings” or “goodbye till later”.
Time and Space:
Subtitles must fit the screen without covering important features of the visual. Further, word limit has to be just right so as to match the readers’ average speed and yet be short enough to be changed in time for the next phrase or sentence. There are many such logistical constraints that have to be borne in mind along with the linguistic, cultural and contextual features.
Subtitles are usually placed at the bottom centre of the screen, but this may be adapted when the bottom of the screen is white in the background or contains other text that is part of the original film and which ought not be obscured. Sometimes subtitles can be right and left aligned to distinguished between the speakers and occasionally be placed on the top or middle of the screen too, to match the requirement.
Subtitles are usually not more than 2 lines in length, each line containing not more than 35 characters (of the roman script). The usual duration of a subtitle is between one and six seconds. However, the most important determinant of the duration and length of subtitles is the comfortable reading speed of an average viewer.