Does anyone know of an immersion Japanese language program during Summer 2020?
Not sure whether you are looking in the US or in Japan. In the US, Middlebury has a very respected Japanese program and they do have a summer course. In Japan, many good universities have immersive summer programs. I’ve linked one in Kyoto and one in Tokyo, along with the Middlebury page.
https://www.middlebury.edu/language-schools/languages/japanese
http://www.kicl.ac.jp/en/summer/
https://www.sophia.ac.jp/eng/admissions/summer/