you can only unregister mainLoop functions.
Just replace the function to kill the action text function.
function FrenchActionText()
end
Or wrap whatever is inside of it in an if query. if condition/value is x.
also quick note: the function doesn't have to be located in the same script containing the line that registers it.
anyway, unregister for mainLoop functions would be like this...
unregisterEventHandler("mainLoop", "example")