"I like the sports."
Translation:Me gustan los deportes.
"el deporte" (instead of "los deportes") was acceptable earlier for "he does not like sports." why is it not acceptable here?
Sports in general can be los deportes or el deporte. But here the English specifies "the sports" which implies some particular subset of sports, rather than sports in general. This requires a definite article in Spanish and it must be plural, which means only "los deportes" works for this one.
However, if you were going from Spanish to English, "Me gustan los deportes" could be either "I like sports (in general)" or, as in this case, "I like the sports". Context would determine which.
A mí me gustan (plural noun) - is the full, proper way to say it.
It's frequently shortened to leave off the "a mí"
No. Gustar means 'to be pleasing to', so with 'me gusta(n)' what you are literally saying is "something is pleasing to me". Since the thing doing the pleasing here (deportes) is plural, the verb 'gustar' must also be plural (gustan).