Wikipedia has a list of selected editions.

The first english edition was in 1963, the first american one in 1964.

FTA: "Mr. President—out last summer in David Unger’s lucid new translation"

I assumed that was a translation into English.

My mistake! The translator name helped me locate the novel:

https://www.kobo.com/us/en/ebook/mr-president-18

It's been translated and is widely available in English. It's an excellent book and one of the most important Latin American novels of the mid-1900s.