What are the politest ways to say "you" in Japanese?
I'd like to know which "you" to say before speaking to someone I don't know yet in Japanese.

Question

Answer

In most situations you can drop the subject (i.e. "you") when it is obvious you are talking about the other person, unlike in English where "you" is used a lot to make the sentence grammatically correct.

For example: 
English: "What is your favourite food?" 
becomes -> 
Japanese: "Favourite food is?" ("your" is implied)

When you know their name, using "last name"-san is generally polite

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