Karsten's basicFunctions.js apparently implements lang.LANGUAGE for adding another language to the Info button.

Currently, line 4 of lang.js in %APPDATA%\nodeeditor\core\lang.js must be changed to (for example) FR, in order for a nodes Info selection to use the French version of the
Info *.html file. (The MoI Option button change to French is not recognized by Info selection.)
To change language to French "FR", use MoI Option button.

New .html documentation information:
So to add Sweep.html documentation for another language, say French, add another folder alongside EN, called FR, path:
%APPDATE%\nodeeditor\nodes\extensions\Documentation\FR (or equivalent Math path.)
After translating Sweep.html, to say SweepFR.html, place SweepFR.html into the FR directory.

The above is tested, and subject to editing :-) EDIT, SOMETHING IS WRONG...Line 4 of lang.js currently needs to be edited, for example to "FR" for French Info .html to work. See Below

- Brian

(As has been explained in other posts, %APPDATA% refers to the users appdata folder and path. My version on windows 10 is here: C:\Users\orcha\AppData\Roaming\Moi )
Mac version is a similar, but a little different.