The historical reason is that French pilots flew with the flying regiment
'Normandie' (later Normandie-Niemen) against the nazis in USSRr during ww2.
Due to the great success of this squadron, Stalin allowed the group to get
back to France in 1945 with its YAK3 fighters.
The squadron still exists and flies Mirage F1CT in Colmar Meyenheim. French
pilots and their russian counterparts remained 'friends', even during the
dark days of cold war.
They participate in exchanges with the russians since the 70s and maybe
earlier. A good deal to evaluate russian aircrafts at this time.

Yann



France downplays jet swap with Russia
France says recent joint maneuvers in which Russian and French pilots
flew each other's aircraft were not an effort to help Russia join NATO
or the European Union, but simply "in the interest of world peace and
cooperation."
http://www.washtimes.com/world/20030...2731-6790r.htm

IIRC, USAF pilots flew most of the European and Asian Air Force planes
- except the U.S. Navy, hehe.
Mike