German is not my native language but I have a lot of experience with it. To translate "because of what he said", I feel like I should say "wegen dem, was er gesagt hat" instead of "wegen dessen, was er gesagt hat". However, I'm unsure because "wegen" usually takes genitive. Both forms have a pretty large number of Google hits. What is right in this case?
In spoken language, I would definitively use the first approach
Wegen dem, was er gesagt hat.
It sounds less formal. Using genetive constructions in spoken language may cause you to be perceived as overly correct in some regions (and depending a lot on your audience, of course).
For written texts, I would take the hint from Ingmar's comment to choose a less literal translation.