I 100% do not think in words or sentences or language. It feels more like node-traversing a graph of concepts, but it's all completely abstract. While I am able to consciously play back my thoughts linguistically or visually with some effort (and at the cost of efficiency), by default there are neither words nor images.
French is my first language, I'm fluent in English, and I know a bit about many languages... But I've never had an inner voice or thought in language, even when I was very young.