What's the meaning of "je t'envie"?
Is it "I want you" or "I am jealous of you"? Or both?
''I envy you.'' Envier translates into English as “to envy”.
However, beware of “avoir envie de” … This is better translated as “to feel like”, for example “j'ai envie d'aller au resto ce soir”.
Definitely no more the first one. While in the 19th century, envier has sometimes been used to mean "to desire", in current French, "I want you" would translate to j'ai besoin de toi or je te veux.
Nowadays, envier means something like "to regret not to be in someone's position, not having something someone has".
It is close but often slightly softer than être jaloux de quelqu'un. Être jaloux is a negative feeling while envier is more neutral.