I found that slightly annoying as well, since elsewhere on the site they translate from French. For mathematicians of a certain age knowing how to read French,

I found that slightly annoying as well, since elsewhere on the site they translate from French. For mathematicians of a certain age knowing how to read French, English, and German is pretty common since often mathematics papers were only available in one language. So, my guess is that because of when the author was educated this is just normal for him.