Programs aren’t written by a single team of developers that speak the same language. You’d be calling a library by a Hungarian with additions from an Indian in a framework developed by Germans based on original work by Mexicans.

If no-one were forcing all of them to use English by only allowing English keywords, they’d name their variables and functions in their local language and cause mayhem to readability.

[Edit:] Even with all keywords being forced to English, there’s often half-localized code.

I can’t find the source right now, but I strongly believe that Steve McConnell has a section in one of his books where he quotes a function commented in French and asks, “Can you tell the pitfall the author is warning you about? It’s something about a NullPointerException”. McConnell then advises against local languages even in comments