There's two different ways how you can add text files. Following file formats are offered when you upload a master file.
This is meant for short texts like app description or marketing content where the translation needs to be a single text document. Document is visible in the editor in a side-by-side mode so it's easy to create good and consistent translation.
For bigger text files or where the content may vary, we recommend using Line Separated version where texts are segmented to similar strings as in any other format.