Can lawyers from other countries practice in the United States?

They have to pass the state bar exam in the state they want to practice. Different states have different laws so they need to know what the laws are for that state. 

No, because they'd have to know US law.  Other countries don't have the same law so they're not going to be any help to a client unless they know the differences.  They'd have to pass the state bar exam, but the state Bar Association or whatever it's called might have exemptions for lawyers qualified in another country.

Which could depend on which country that is.  US law is basically a common law system which is based on English law, so an English barrister or solicitor will know the basics of how It works and maybe could get away with a short conversion course.  A lawyer from a country with a more different legal system would have to do more to get through the exam and probably have to go back to law school for longer.

I can't be certain as it's different laws in every state, but that's essentially how it would go.

Even US attorneys must be licensed in EACH STATE where they intend to practice.

Having a license in one jurisdiction often allows a streamlined process to receive a license in another, but you still have to jump through some legal hoops.

probably not because US does not approve a university degree from a foreign country.  A lot of cab drivers from India are doctors and they cant practice in the us.

Im not a lawyer but I play one sometimes .  They may have to pass a state bar exam to practice here .