an unorthodox approach to movie dubbing used by Danny DeVito, one of the stars of the animated film, is also lending his voice to the Italian, Spanish, German and Russian versions.
Mr. DeVito doesn't speak these languages, so he worked with voiceover actors for the various languages (the people who would normally be doing the recordings themselves) to learn lines and practice pronunciation for each one.

The orthodox approach for voice over is as with interpreting, native speakers are considered the best bet when it comes to delivering voiceovers.  Intonation, timing, pizzazz, and the myriad other components that make for a well-done acting job are infinitely easier to accomplish in a language you speak with total comfort.  These factors are even more vital in an acting situation than an interpreting one, since entertainment, as well as, information are key.

source: translationbydesign.com

When Universal's "The Lorax" goes out to Italo auds in March, local auds will experience something rare: a Hollywood star dubbing himself in Italian.
Danny DeVito -- who voices the titular furry creature in the Dr. Seuss adaptation -- will also be dubbing himself in German for the first time.
Usually, local stars are used to dub studio films in their home territories, but this mini-trend of Hollywood talent tackling the lingua franca in which their films are playing seems to have begun in Italy.
Antonio Banderas did his own voiceover track in Italian, and also, naturally, in Spanish, for DreamWorks' "Shrek" franchise, as well as for Universal's "Puss in Boots," which did some $20 million in Italy for U, thanks partly to the dub.
"After Banderas, producer Chris Meledandri proposed that we do the same thing with Danny DeVito in 'Lorax,' " says Paolo Mangiavacchi, Universal Italy film operations director. The point was written into DeVito's contract.
"Danny speaks some Italian; but less than Antonio," Mangiavacchi notes. DeVito presumably knows even less German.
But there are ways to provide high-wattage voice talent with a foreign-language speed course of sorts. First a guide track is recorded with a local dubber, which the Hollywood star can work with in an L.A. studio. And local dubbing directors are flown to Los Angeles to supervise and act as voice coaches.
Also, going native is not the point.
In DeVito's case, his Brooklyn accent remains very strong. "But, within the story, it works; in fact it's a key element of 'Lorax' even in Italian," Mangiavacchi says. "Whenever you have Hollywood stars willing to do this, it helps us re-create the same flavor as the original." Even though, he is quick to add, local dubbers are great.
Source : www.variety.com/article/VR1118049381

My self I have experience so well as a voice talent, voice over in greek, german, french, english and greek :

www.elef.gr/en/voiceoversadubbing.html
 
Cultural consulting and a coach function for managers wishing to address a presentation or speak directly in french for workers representatives or sales teams in Paris, Lyon or near Rouen is requested as well in France. At another occasion a financial manager of a Holding working in Germany used my services even thought he spoke himself sufficient french for everyday affaires, hired my services for a period over one year during internal meetings and an internal company film.

Nouvelle pratique: Danny DeVito. Il a lui-même doublé sa voix!

La voix derrière Lorax, c’est celle de Danny DeVito. Il a lui-même doublé sa voix en espagnol, en italien, en allemand et en russe. Ça ne prouve pas qu’il soit polyglotte, mais qu'il est bien suivie par de talents de voix , des traducteurs interprètes et qu'il utilise ce tremplin pour avoir encore plus de succès, accent, timbre et cachet dans ses prestations de voix.