Finally got the French version of Info documentation to work.
I used Planar from the Construct2 as an example.

Lesson 1, Create (or translate), a French version of Planar.html, and place the file in the FR folder under the nodeeditor Documentation folder.
Do NOT change the name Planar.html.

Lesson 2, (I could be mistaken, but:) Apparently Karsten's code does not utilize the MoI Option button language version.
So changing "EN" to "FR" in line 4 of lang.js was used to enable Info to access French version of Planar.html in the FR directory.

???This should be corrected by modifying the prototype.getExtraMenuOptions code??? to recognize the MoI language being used as per the Option button language version selection. (Somehow, I do not know how.)

- Brian
(My French Planar.html file was just titled as a pretend translation.)