In Spanish the subject can be skipped (Yo juego = juego). Is it okay to skip it in English?
*given that the subject was previously stated in the conversation*

See a translation

Never in written English. Sometimes in spoken, colloquial/informal situations. It is hard to make a rule for it, but it usually occurs when the subject is clearly understood by context.

For example, let's say you call a friend on the phone and ask if he or she would like to join you for lunch. You would typically say something like, "Hey, wanna have lunch today?"

Wanna = informal way of saying "want to"

Here, the 'you' is understood because of the context (informal, you are obviously talking to the other person and no one else).

There are many situations like this in informal speech where this happens frequently. It's never taught formally (as it is always incorrect formally), so I don't now how to describe it with a rule. But watch lots of TV shows and movies and you will develop an intuitive sense for it. You do absolutely need to know how to deal such spoken constructions, because they are the stuff of everyday English conversation.