I adore Francois. Any time he appears in a movie is okay with me!
(My sister and I were early foreign film buffs together, and one night as we were discussing French films I accidentally called him "Trancois Fruttaut." I'll never get out of my head, darn it.)

A central theme of the movie is communication problems. Truffaut barely speaks English so is ideal for the part. He speaks a lot of French, most of which is not subtitled. The audience is left to work out what is said themselves. This mirrors the humans trying to speak to the alien ships and not fully understanding the musical responses.
They resort to using sign language to communicate at the end.

Truffaut was excellent in the role. I saw the film again a couple of days ago, not having seen it for years. If the movie disappointed me, Truffaut's performance didn't. Made it that much sadder he died so young and so many movies he might have made were lost.

It also gave almost all of the conversations he was in a sort of suspense because you had to wait for the translation to understand what was being said. That small moment where the audience is left hanging created some tension and suspense,
Couldn't agree more, and Bob Balaban did a nice job as the interpreter, too.

good points. agree, the translation part was cool.
also, orson welles should have gotten a part.
The food I've liked in my time is American country cookin'-Colonel Sanders

I don't know the exact reason but I thought it was a great casting. It also gave almost all of the conversations he was in a sort of suspense because you had to wait for the translation to understand what was being said. That small moment where the audience is left hanging created some tension and suspense, at least for me it did.

As we know, Bob Balaban later changed his name to Russell and joined Greenpeace.

I liked him and Bob Balaban in this. Great casting!
Books has no sound

I think the casting of Truffaut was perfect, having this globe-trotting French guy, heading the scientific investigation into the outbreak of mysterious phenomena associated with the alien sightings and encounters. It reinforces a more global perspective to the story, than if the Lacombe character had just been some kind of US Air Force officer, or the like.

This message has been deleted.

As described by Teri Garr and others in the Making of Close Encounters documentary, Truffaut was a film fanatic, obsessed with all aspects of film making. Well versed in every genre possible, he even knew about an obscure film called Red Line 7000, in which Garr appeared in a tiny part as a dancer. Memorized the plot, cast and director and someone speaking fake French.
Truffaut also gave praise to production designer Joe Alves for the tiny little set he'd created that was used as a motel room Jillian was in for less than a minute.
Garr was convinced that all Truffaut ever did was watch TV and movies 24/7.

cool. good to hear! thx.

Not that I ever heard. Spielberg just thought he was right for the role and offered it to him.