Internal language is observable and real. But the vast vast majority of what the 90,000,000 neurons that specially compute when you read this sentence are being intelligent too (and most of what they compute could be spoken if your underlying intelligence brought them to mind.) This is also observable and real.

Obviously, if Language is the carrier of intelligence (which is what I wrote), then language can carry intelligence, and does so, more exquisitely than any other mode of communication. LLMs are still showing what Chomsky taught as 'surface level' intelligence with a smattering of 'deep level'. Our knowledge of how to get them to show deeper levels of intelligence is pretty well understood. The problem is that we don't have hardware that can do the 300 trillion fundamental computations that our brains routinely do. Those 90M neurons have 3,000 synapses each on average. 100B neuron in the brain have the 300 trillion standing ready with even more intelligence about what is perceived or done. Much of it able to speak but no time, or reason, to do it.