"There is a depth of thought untouched by words, and deeper still a depth of formless feeling untouched by thought." - Rilke

Your assertion that we don't think in language is questionable. It runs counter to the lived experience of developing thoughts through writing ("writing isn't capturing thinking -- it is thinking"). I believe there is more to thought than language alone, but I also feel quite sure that language forms an essential part of thinking beyond a base layer of instinctive animalistic associations. Sophisticated thoughts are impossible to construct or maintain in the absence of language to represent concepts.

Edt to add: I cited Rilke because I find the notion [some deep thoughts are beyond language] interesting. But I disagree with the idea that language is only ever epiphenomenal (co-occurring with thought), or akin to a hard-of-hearing scribe attempting to convey thoughts which always have independent existence.