It's depend on verb! You can say "parlo l'italiano" and this has the shade of "i'm able to speak Italian" (by the way, this is the only case (name of languages) in which "parlare" can be transitive. You can say also "parlo in italiano" with the shade of ("I speak using Italian") as well as "parlo italiano", in this case "italiano" is used as adverb: "I speak """Italianly"""". But you can't say "sto imparando italiano" because "imparare" is strictly transitive and requires a definite object.

Better: Sto imparando l'italiano. And no, sometimes you can omit "il", so you can both say: "Parlo italiano" (more current in italian) or "Parlo l'italiano". Francesco

The second one is correct. When you say "sto imparando italiano" here "italiano" is an adjectif and there is not a noun to which it refers. You have to use the article because the sencence sounds like " io sto imparando la lingua italiana" and "italiano" is used as noun. I hope helped you.

The followings are correct forms, what you see in [...] is optional. Parli [l'] italiano ? Sai parlare l'italiano ? (if you use Per favore, parla in italiano, dato che sai farlo. Mi piace parlare in italiano. Sto imparando l'italiano Sto imparando la lingua italiana. As you can see in this case (that would also apply to 'inglese' or 'francese'), the context makes the difference. Actually if you ask educated natives, well ..., we all agree!

Thanks everybody!