Does a Nandroid Backup contain Language files?
As a Nandroid backup creates images of all Android related partitions of the device (not of the radio-firmware, which is not directly related to any OS), your assumptions are correct: it covers everything, i.e. all data belonging to the Android installation. So provided both of you use the exact same device (compare the specs, some devices have variants which could be crucial when involving different hardware components), the copy as described in the question should work.

To be on the safe side, and have a chance to revert back, it cannot hurt to create a Nandroid backup on the target device as well, though :)