Mike is correct in his information regarding Benson Fong. The restaurant that Mike mentioned, "Ah Fong's," was a regular meeting place for a good number of Hollywood stars. I used to correspond with a person who knew Mr. Fong and his restaurant (Her son called him "Uncle Ben.") and she had some fun things to relate about him and his eatery.
Now, as to Victor Sen Yung, you bring up a very good question. Throughout the Charlie Chan series at Fox, he was billed as Sen Yung. Then, after the series had moved to Monogram, He was called Victor Sen Yung. Why this was so, exactly, I cannot say. Probably it was at the suggestion of the studio that his first name be added, or, maybe it was at Mr. Yung's request. This would be a good subject for some research, perhaps!
I'm thinking part of the reason for the name change was to "Americanize" himself to get more work as an actor. I believe there are others that have done the same thing, though none come to mind.
Back in 1991 I went to a Sci-Fi Convention to see actor John Levene. He's known to Doctor Who Fans as Sgt. Benton of U.N.I.T. While talking with him I found out he had acquired a "stage name" of John Anthony Blake saying it was more of an American name. I don't know offhand if it worked though...