James Cameron’s Avatar has earned about $600 million at the domestic box office but has raked in more than twice that much internationally. The viewing experience in many non-English-speaking countries is naturally quite different—since audiences hear dubbing artists read Sam Worthington and Sigourney Weaver’s lines. While Americans generally associate dubbing with out-of-sync martial arts B-movies, the technique is no joke for audiences around the world, where most of the big-budget films are from the United States. How does dubbing work?
First, pick your languages. Big Hollywood movies are always dubbed into French, German, and Spanish, since those respective countries all have sizable film-going communities. There are often two Spanish versions, one for Spain and one for Latin America. Otherwise, the decision depends on the type of film and its 
perceived market value in a given country. Animated films are dubbed into more languages than live action, since animation is primarily aimed at children who may not be able to read subtitles. Disney’s The Princess and the Frog, for instance, will be dubbed into 38 languages, while the studio’s live-action offering The Sorcerer’s Apprentice is only scheduled for nine.
The studio then hires translators, who typically reside in the local country. They start by creating a raw, word-for-word translation. In many cases, the translation is then tweaked to make the words fit better with the actors’ English-speaking mouths. The translator will try to make the “labials”—the consonants that cause the mouth to close, such as M, B, and P—match up with the labials in the English version.
You said “labials”. :0