vBulletin Manual - Downloading and Uploading Languages

Languages can be downloaded (exported) and uploaded (imported) like styles. This allows you to share your translations with others or use someone else’s translation to save time. To upload or download a language, go to Languages & Phrases > Download / Upload Languages.

To download a language, simply select it and an appropriate filename and click [Download].

Note:

Only translated phrases will be in a downloaded language.

Language Source – the first two options represent the source of the language, a file you upload or a file that is already on the server. If you do not specify a file to upload, it will assume that you are importing the file off the server.
Overwrite Language – if you select a language here, that language will be overwritten with the uploaded language. Otherwise, a new language will be created. This is useful if you are importing a newer version of an existing language.
Title for Uploaded Language – if you are creating a new language, you may specify a title for it here. You may leave this option blank to use the title in the language file.
Ignore Language Version – if you leave this at no, then an error message will be displayed and the language will not be imported if it was created for a different version of vBulletin. Set this to yes to disable this error checking.
Warning:
Language data generally changes from version to version. Thus, if you are importing a language from an older version, these differences may cause problems.