Tcl does not have GIL and is possibly one of the most dynamic languages that has seen nontrivial use. Guile does not have GIL. Running multiple interpreterd in different threads is a common notion in Tcl.
Running multiple sub-interpreters in different threads is easy in Tcl, but it doesn't stop there. If you want, you can run multiple threads in a single interpreter, using locks mutexes, etc., if you're inclined to take on the attendant complexity and risks.
Ability to run a separate interpreter per thread was designed as a handy simplification, so you could sidestep the usual complexity of thread programming if you wanted.
Ability to run a separate interpreter per thread was designed as a handy simplification, so you could sidestep the usual complexity of thread programming if you wanted.