In my Japanese novel, the first time any dialogue appeared, I mentioned they were speaking Japanese. Then I used English with scattered phrases of Japanese in italics. In spots where they shifted back and forth between the two languages, I had to use the tag you mentioned, but I used it sparingly. It can be done, Dirk. You have to be careful not to overwhelm anyone with "he said in Japanese" tags.
As a secondary thought, if you self-publish through Kindle/Amazon, keep in mind that not all languages (and fonts for those languages) are supported.
Bill