In the French version, however, Marty doesn’t sport Calvin Klein underwear.
The change was made presumably under the assumption that the name Pierre Cardin would be more familiar to French audiences than that of the New-York-City-based Calvin Klein.
Rather, his boxer briefs, we are told, are Pierre Cardin, and Lorraine goes on to refer to Marty as Pierre.
In the original version of the movie, that name is Calvin Klein, and Marty is thus known to Lorraine as Calvin.