You watched Pearl Harbor didn't you?  

'39-41 over the channel... none. 
there were of course a variety of foreign planes on hand being evaluated, but not in operational combat.
109e/110c/stuka vs spit/hurri1 is it as represented by the planeset we have.  '42 and beyond is when you see american stuff getting into the mix. The Brits utilized most of the lend-lease stuff in the Pac, anyway.
If you want to see a mix, your best best is to look at the eastern front in '42-43... or the CBI/Pacific.
<edit: also take a look at the African/Med/Italian campaigns.)