Two sentences.

By adding "も", in the first sentence, the sentence means that Mr.Suzuki can't speak Chinese thoroughly. If there is not "も", the meaning is not clear.

In the second sentence, by adding "しか" the sentence means that he can speak German only. But if there is not "しか", so this meaning turns into that he can't speak German. But in this case, usually Japanese use "が" instead of "しか" and it's expressed next sentence;

彼はドイツ語ができません．