Your example misses the mark as "silly" can be explained in German and Gemütlichkeit can be explained in English.

Language structures our thoughts. It is claimed that Chinese are better at math because of their language structure. How you express things in a different language will help you more clearly see the concept in your own language. I learned more about English by learning German than I did in all my schooling. It improved my spelling as well because it made me understand the words I was using better.

It's not about explanatory power, it's about patterns of thinking. Americans call each other "silly" all the time, but I'm guessing German's don't. Even though it's possible, it takes more effort, and doesn't come to mind as readily.

They could call each other "lustig" or "lecherlich", which often covers what is meant by silly.