I was at Computer Corporation of America for a few years, until 1988, in the research group. It was quite illustrious in its day, producing very interesting research and prototypes, (concurrency control, extended relational databases, the Adaplex project). We were aware of both the 5th Generation project, and the US "competitor", MCC.
Remember, at the time, Japan was an economic and technical powerhouse, There were concerns about the Japanese buying up valuable real estate in New York. We were worried about the trade imbalance. So 5GP was quite threatening to some.
I remember meeting one of the 5GP researchers who credited MCC for scaring the Japanese into greatly increasing funding for computer science in his country. And one of the other comments here pointed out that the fear worked in the other direction too.
Another commenter here talked about Prolog. One of the lines of research at the time was on "expert systems", and if I remember correctly, Prolog was one of the major languages for research in that area. An expert system was a set of rules for solving a problem in some domain. It was yet another failed attempt at AI, which didn't really work beyond toy problems. (Of course, now, those rules come out of machine learning systems, but the rules are kind of inscrutable.)