Internationally 1984, according to this, https://en.wikipedia.org/wiki/ISO_7736I do know that DIN originated in Europe, Germany if I'm not mistaken.
However, I'm sure they were gradually appearing on the European market before that, with Blaupunkt being one of the first to be available in DIN, as a dealer fitment / upgrade, usually on Mercs and Jags. Oh, the fun involved in carefully enlarging the dash holes to take the DIN cage, on a v. expensive car.