David Laughlin is the guy that follows Lacombe everywhere he goes like a bearded, bespectacled beagle. At first glance, his role in Close Encounters is simple: He's a translator, so he says everything Lacombe does but in English. Nothing too complicated here, right?
But when you consider how important the theme of communication is to the film, his role becomes critical. As a translator, his job is to help others overcome difficulties of communication, specifically those resulting from people speaking different languages.
PROJECT LEADER: Can you translate French into English and English into French?
LAUGHLIN: Yes. Yes, I explained it to the team leader. I'm just a little taken by surprise.
LACOMBE: Etes-vous Monsieur Loglin?
LAUGHLIN: Laughlin, oui.
LACOMBE: Oh, Laughlin. Pardon.
As the two spend time together, Laughlin fits into his groove as a translator and becomes inseparable from the French scientist. Thanks to Laughlin's translations, Lacombe's able to work with the English-speaking research team. Sometimes, there are as many as three different languages involved in trying to speak with the locals. For example, when the research team visits India, it's French to English, English to Hindi, Hindi back to English, English back to French.
Laughlin hasn't always been a translator. His former occupation was cartography, i.e. mapmaking, and this comes in mighty handy. Evidently, the aliens speak longitude. When the research team begins transmitting the five-tone phrase into space, they receive a series of numbers that seem random at first. But Laughlin has an aha! moment:
LAUGHLIN: Excuse me. Excuse me. Before I got paid to speak French, I used to read maps. This first number is a longitude. Yeah. Two sets of three numbers: degrees, minutes and seconds. And the first number has three digits and the last two are below 60. Obviously, it's not in the right ascension and declination on the sky. These have to be Earth coordinates.
Laughlin's cartographic insight drives the rest of the film's plot. He sticks by Lacombe as the scientist coordinates the alien encounter and watches in awe with everyone else at the momentous event.
Bob Balaban, the actor who plays Laughlin, had to lie about his command of French in order to get the role. At his audition, he mouthed some French he quickly learned and hoped no one else on the set spoke French.
Balaban couldn't believe he was working alongside legendary director Truffaut as well as being directed by budding superstar Spielberg. He knew something like this might not ever happen again to him, so he kept a diary during the filming. Since no press were allowed on the set, the diary's an intimate look at what it was like to make this movie. He published it and issued an updated version on the 30th anniversary of the film.