Translation:Tell me who you walk with, and I'll tell you who you are.
But that means that similar people hang out together, whereas in my opinion, the Spanish is saying that you can judge a person by the company they keep - it doesn't mean that you are the same as your friends though. For instance, a coward may hang out with someone who is brave to avoid having to stand up to people (simplified example!)
It was the pig fair last September The day I well remember I was walking up and down in drunken pride When my knees began to flutter And I sank down in the gutter And a pig came up and lay down by my side As I lay there in the gutter Thinking thoughts I could not utter I thought I heard a passing lady say You can tell the man who boozes By the company that he chooses And the pig got up and slowly walked away
A man is known by the company he keeps - It's kind of an excerpt from a Ralph Waldo Emerson quote about how to judge a man's character.
Anyway, "You can tell a person's character by the company he/she keeps." This could be negative or positive; it's saying how you can tell. Basically if you spend time with jerks, you're probably a jerk. If you spend time with good people you're more likely to be a good person. This is both a warning and advice in judging whether someone else is good company.
Do you want them as a friend if all their friends are jerks? Do you want to be thought of as a jerk-by-association if you spend time with jerks? Same thing with any similar kind of traits: stupid or smart people, angry or happy people, tolerant or impatient. If you want to be raised up to be better than you could be by yourself, surround yourself with great men and women.
So it has a lot of implied meaning as well.
A Mexican lady who loves proverbs, adages and idioms loaned me a small book filled with them. "Dime con quién andas, y te diré quién eres." was in this booklet. The translation was: "Birds of a feather flock together." DL did not accept this cultural equivalent, though many other sources not only accept it, but TEACH it.
It's interesting to read these comments and see how many people are worried about the technical grammatical translation, and not about the meaning of the idiom itself. Language is about meaning, is it not?
It rarely makes any sense to translate idioms and expressions word for word. Instead, you want to identify the equivalent expression in the target language.
In this case, the most well-known comparable idiom (in my opinion) is "Birds of a feather flock together."
They both carry the same intended message: You tend to be like those you spend the most time with. If you fly with geese, I can assure you that you are not an eagle. The natural consequence of this meaning is that if you don't like who you are becoming, then it's time to find a new "flock" that closely resembles who you would like to become.
I've never heard anybody use the phrase "Tell me who your friends are and I'll tell you who you are" in English, except when trying to translate this Mexican idiom.