I think language is required for communicative sentience, but not for consciousness - I mean, bees are obviously conscious. Sense of self, doubtful - but certainly present in other higher order vertebrates.

Unconscious intelligence is vastly underrated. I learned to use mine, early on. Consciously, I’m kinda average cognitionwise - but I figured out many years ago that if I just go with the first answer that tumbles into my head from seemingly nowhere, it’s usually right, and the moment I start consciously thinking, it goes wrong. It’s like trying to catch yourself looking elsewhere in the mirror - you can’t ask directly, but the computer already has the answer long before your language driven abstraction layer can grind there.

See also: savants.