"I like the mountains."
No it is not wrong cause he is talking generally
We say: "احب البحر" و ليس "احب البحار".
Also: "احب الشاطئ" و ليس "احب الشواطئ".
May want to run that past the Department of Arabic at the American University in Cairo. Without context and the fact the isolated sentence uses "mountains" in the English sentence while using the singular form of the word in MSA... I am not certain that the sentences are in agreement. The mechanism you mentioned exists in American English. In Am. Eng., while it is a generalization, it does not act as a collective noun - it just infers the general experience of "the sea" or any sea. In Am. Eng. There is also a subtle difference in I love the sea ( as an experience of the sea) and the sentence "I love the seas". I love the seas relates the meaning that you love each individual sea with all their unique and shared characteristics. If you hear this is Am. Eng the listener does well to verify the speakers meaning or risks accepting an Over Generalization as fact.
If you want plural you must use plural. This mechanism does occur with the word "sea (the sea)" just as you cited in Arabic. This mechanism is not utilzed with the word mountain or phrase "the mountain".
I agree 100 percent. Charles describes the issue perfectly - and it is not easy to describe. In the second case, it's the same. In English you would never say I love the coasts. Interesting to know that this is being developed at the Arabic Department in UAC!