Are you sure? I never heard that he did that with his Silent movies, there was usually no need. Sound movies, yes, there's the french version of M and Das Testament des Dr. Mabuse, I don't think Metropolis got that treatment, though. Correct me if I'm mistaken...
Actually, we're both right. Early sound pictures were indeed filmed several times in different languages, because sound processes in the early Talkie era was so pricey and complex that it was more cost effective to just shoot everything multiple times in different languages (Browning's "Dracula," and Dreyer's "Vampyr" being two such famous examples).
But it was also common practice during the silent era to capture a scene with two or more cameras. Often in behind the scenes or production photos from the era, you'll see several cameramen lined up, all capturing the same thing (apologies for the low res)Silent Film Production
This was due to the fact that at the time, quality dupe stocks did not exist, and so prints had to be made directly from the camera negative. Depending on the popularity of the film, the negative might see a lot of wear and tear (legend has it that the original neg for "The Birth of a Nation" was literally worn out from the demand for prints). The solution was to produce two camera negatives for domestic and international markets, thereby halving the amount of use each negative would receive.
This meant then, that the domestic and international versions of any given film might differ radically from each other...different angles, different takes. Compare the 1925 version of Phantom of the Opera with the 1929 version. The surviving prints of the '25 version were likely derived from the domestic negative, while the '29 version was most likely produced from the international print (though this is still debated). The '29 was a re-release and was both shortened and reedited, but the scenes that remain the same between the two still differ. The unmasking scene, for example, uses different takes and different angles. It makes for a fascinating study in editorial decision-making.
Hence my argument for the inclusion of the entire Argentine print of "Metropolis." It is known that at least two camera negatives were produced, and the 2001 Murnau restoration was a hybrid of the best survivng material from the extant negs and prints, and therefore, not necessarily "pure," unlike the Argentine print, which all evidence suggests is 100% original (save for one scene that was lost due to it being at the end of a reel). It is a very real possibility that the new print, in addition to the scenes not found anywhere else (some 20-25 minutes worth) other shots and perhaps whole scenes and sequences could contain alternate takes and angles that do not exist ANYWHERE else.
Which is why I think Kino REALLY ought to release a definitive set. Metropolis has just about the most complex version history of any film apart from just about everything Orson Welles ever made, and any definitive DVD edition ought to emphasize this. It ought to include the U.S. version, which, corrupt though it may be, is the version the film that most of us were exposed to (myself included). It is in the public domain, though finding a quality print would be a challenge. Then, you could have the complete Argentine print, which could be called the "original" version, and finally, a definitive "restoration" combining all the best surviving elements to create the closest possible approximation to the film that premiered in 1927.
Well, I've gone on too long!