The folders in languages/ contain the translated language strings used by this plugin.
If your language is one of NodeBB's supported languages (check to see if it is listed here).
If so, then great! Create a pull request containing a new folder with the same language code (e.g. "de" for German), containing the file 2factor.json. It is easiest to just copy one of the existing files and translate it into your own language.
Submit the PR, and if all is well, I will accept and publish a new version with the langauge included. That's all :)