The simplest being my proposal that was a variation on my scheme for bouncing packets/messages across many non-cooperating, national jurisdictions a decade ago. That is: diversity with mutually-suspicious or competing parties. The hardware and software comes from different people, fabs, and nationalities. Preferably that compete. You run the same verifiable core on all of them with lots of tests for equivalence. Build non-optimizing compiler in that from readable source. Build optimizing one with that.
With about 5... esp U.S., French, Russian, Chinese, and Japanese... you should be fine. Add South Korea these days with Samsung hardware. The software doesn't have to come from same countries as hardware. Better if it doesn't. All safety checks on in it with POLA enforced at the least. Shady exploits based on language primitives (esp C's) is why the compilers need to be in safe languages.
With about 5... esp U.S., French, Russian, Chinese, and Japanese... you should be fine. Add South Korea these days with Samsung hardware. The software doesn't have to come from same countries as hardware. Better if it doesn't. All safety checks on in it with POLA enforced at the least. Shady exploits based on language primitives (esp C's) is why the compilers need to be in safe languages.