I know that Rimsky-Korsadoff's aria "Song of the Viking Guest" from
Sadko is a Russian work.  However, I also know that the Russians
flirted greatly with the French (politically, artistically, etc.)
during the period of it's compostion.  And, due to this, many of the
Russian nobility and artists spoke french.  So, my question is, did
Rimsky-Korsakoff originally compose and then set "Song of the Viking
Guest" with both Russian AND French options?  I need to know this
because I would like to sing it in french in a competition in which
one may only sing works in their 'original language'.  Thanks : )

Interesting question! I've emailed a friend who is a Rimsky-Korsakov
fanatic. I'll let you know if I learn anything.

I've received a response from my friend who knows a lot about
Rimsky-Korsakov. Unfortunately, he says he does not think that
Rimsky-Korsakov or his collaborators wrote a French text for "Sadko."
Your French translation of the aria is, in my friend's opinion, likely
to have come from a later time.

I hope another Researcher can find better news for you.

Wikipedia says that the libretto was in Russian by Rimsky-K with help.

http://en.wikipedia.org/wiki/Sadko

Since all his operas deal with Russia, folklore, etc., it seems very
unlikely that any of them would not have had a Russsian libretto.

Sorry not to be able to help you better, Myoarin