It’s easy to learn Spanish and Italian

Question

As I understand it, the first & the second sentences are correct and common. What about the third and the fourth sentences, especially the third one? Is it good to use "it's" if after it are several subjects? What is the alternative if the third sentence is wrong?

It’s easy to learn Spanish.

Spanish is easy to learn.

It’s easy to learn Spanish and Italian, especially one after another.

Spanish and Italian are easy to learn , especially one after another.

Answer 1

They are all fine. The dummy pronouns refer (vaguely) to "the learning" and are correctly singular.

The constructions "It's easy" and "It's difficult" are idiomatic. You shouldn't really think of the word "It" as having any precise reference. Just learn the construction "It's easy to XXX"