Hi Alex,
As most folks here will tell you, the foods he may want to avoid include those with a lot of acid or pepper "bite" to them, as it will make his tongue sting. He will want to experiment with old favorites like tomato sauces and lemon/pepper sauces to see if he will tolerate them or if they are too much for his tongue to take. I personally would avoid any foods which, in the past, have given him indigestion or a lot of gas. In other words, it's a very personalized thing, but he will let you know what he wants and likes.
Glad he has progressed to a point where this has become an issue!

Live well,
Andrea