What was the predominant sentiment regarding the language of instruction in American schools after WWI?

After WW1, there was a significant Nativist movement: anti-black, anti-immigrant, pro-"family values." This was the heydey of the Klan, as well.

It caused the end of a lot of non-English instruction (French in some parts of Louisiana and New England, and several northern Euro languages in the prairies. Not sure how/if Spanish was affected in the SW).

Many presidents of the time supported some variation of the view, but Wilson really comes to mind as a particular supporter.

Predominant sentiment? There was none! There was never any question about that. It was English, is English, and always will be English. Except in maybe 50 years, when Spanish will be the most common language spoken in the USA. It's heading that way. In the UK, it will be Arabic.

I don't understand your question. Instruction in American schools has always been in English, before and after WW1.