I don't want to speak on JT's behalf, but I can answer the language barrier part. Barney Miller was a 70's tv show set in a police station. It was relatively low budget and the studio setting didn't look anything like a real precinct. The term "cheesy" means a lot of things, in this case, basically cheap looking. A "mock up" is a low quality imitation of something.

So JT is turned off that the "gotcha" scene, the climax of the episode, is filmed in such a low quality studio setting, especially after the rest of the episode was shot either on-location, or with high quality settings. Personally, I never noticed it, but now that he mentions it, I see his point.

There was also a running joke on BARNEY MILLER about the office being full of outdated equipment and office supplies. So some of the things that would look dated to people were meant to actually look that way while the show was on the air.

Thank you, Pete. Yes, you've correctly (and succinctly, I might add) summarized exactly what I was saying. The ending to this reminds me of the ending to "A Friend in Deed" - wonderful on location footage - the houses, the bar/pool parlor, the commissioner's office, the helicopter - and then they revert to a cheesy (cheap, obviously fake) set on the studio lot to finish one of the best episodes of the entire series. It sort of kills the moment for me every time I watch - I want to shake the director and yell, "Why??? Why??? Why this stupid set when you could have finished it somewhere more appropriate?"

But that's just me.