The synonymous sentence that they work in the German library can be changed in this way. The first sentence can be changed to the place where they work is the library. Then the main Chinese meaning of this sentence is that the place where they work is the library.

Because the words in the original sentence themselves express a meaning, if you work in a library and then convert it into a synonymous sentence, you can first convert it from Chinese sentence to English, and then change it into a different sentence according to different word order and different tone.

Then the second sentence can be that they are working in the library at this time. So in this sentence, it means that they are working in the library at this time, and they can also appear here as synonymous sentences.