While it was definitely used sometime before 1986, it seems like English-language journalists finally became comfortable with the phrase "group of death" in the lead-up to the Mexico World Cup.
The earliest primary source mention in English I could find was in a travel column from the Times of London written on May 12, 1986, by Alan Franks. In the aftermath of the 8.0-magnitude earthquake that hit Mexico City in 1985, Franks tried to give his World Cup-going readers some alternatives to a city he claimed "was never much to write home about even before the earthquake."
They could go to places like, say, Queretaro instead.