If regional commands have any object, then it would be to keep a core staff familiar with the different facets of the region. Not running ops from a Central Command in Florida. The current Unified Commands probably have too diverse areas under their hat (esp CENTCOM). Another problem are up-or-out promotions.

Since the globish-speaking "world culture" is quite popular abroad working in cooperation with regional forces might be easier than teaching some NCO or 2Lt Farsi. But doesn't mean that they shouldn't have the opportunity to do so!

The analogy with the British army has the problem that the U.S. armed forces do not yet have indigenous units with indigenous NCOs. And the British Empire was much more based on trade than on armies. Key was the navy, and I don't think that they bothered to learn local languages.