without even looking i would almost guarantee that the only languages used to write os's would be Assembler, C, C++ and ADA

Pretty much every other language is either OS dependent or has a runtime that OS dependent

and there isnt any way to write an OS in a language that is runtime dependent because runtimes are dependent on OS's thats why for .net to run on diffrent OS's it has to have an implementation of the .net CLR on any OS it wants to run on.
(i.e. mono)