Omega Underground revealed multiple Avengers 4 casting calls looking for Japanese extras (including Yakuza) pointing towards a Japanese setting in the sequel.
The first set photos from Atlanta via AtlantaFilming have confirmed some of the film will be taking place in Japan.

We’ll be keeping an eye out for Scarlett Johansson‘s Black Widow.
Avengers 4 is set for release in May 2019.
SOURCE: ATLANTA FILMING