Translation is the process by which the UI text of software, or the text of the support materials, is translated into the target language. Translation is thus one of the activities that comprises software localization.
The process of translation begins when the source texts are in a format that the translator can handle (often using specialized translation software) and ends when those texts are now written in the target language. Everything that comes before and after this is part of the broader localization process.
Does anyone refer to it as "T9N"? We haven't seen it yet - but perhaps someone will follow the lead here...