I looked at the code/documentation and it seems the intention is to do the reverse lookup, that is look at the buffer encoding and decide what to give inputenc as argument (when it is specified as "AUTO" in the header template). I maintain that the other way around (looking at the header template and deciding the coding system) is probably easier to understand and it is also what's already been used by Emacs: see latexenc-find-file-coding-system and latex-inputenc-coding-alist.
Regards, Achim. -- +<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+ DIY Stuff: http://Synth.Stromeko.net/DIY.html