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If you use XOOPS 2.3.x (do also the security update to the 2.3.2a), you may only copy the subdirectories that do not already exist, otherwise you will overwrite code of 2.3.x, such as art and textsanitiser.
The instructions are for adding more languages to some of the parts in Frameworks. Mosttimes these are not highly visible and you can let it work in English only. As explained you have to copy english.php etc to eg french.php etc and then translate all the text definitions that are inside.
You have to look also once on XOOPSfr.org, which has many translations. Even if there isn't the latest version, it may give you an headstart.
For all the plugins of transfer (subdirectories of /Frameworks/transfer/plugin) there is also a language file to copy (and to translate) and a config file where you can disable the plugin or define the display order.
Most things run from their default settings. It is enough to copy the language files to your language. If you don't bother about some english here and there, a renamed copy is enough and prevent problems with some items.