Hans Wilsdorf began his watch selling business in England.
He bought watches from Switzerland and put the names of jewelers on the dials.
Eventually, he began to put the name Rolex on his watch dials and then required jewelers to buy a Rolex or two for every few watches they bought with their names on the dials.
During WWI, Wilsdorf packed up his business and moved to Switzerland to avoid the high taxes of the time.
I would imagine that by the time Wilsdorf went international with his watches, there was no reason to use any other language on the dials or perhaps it was too cumbersome.
They do use other languages on the day wheels, but that's only been since the 50s
And then, of course, there's Adam's explanation, which is probably the correct one.
