I accept "mangoes" because of the English rule that nouns that end in a consonant followed by a vowel should be padded with another vowel ("e") before the "-s". Another example I can think of off the top of my head is "heroes", not "heros".
However, I also accept "mangos" because it feels right. Wiktionary says "mango" is Portuguese, and I don't know Portuguese, but at least in Spanish you don't pluralize with "-es", just "-s".
When life gives you mangos, don’t make mangonade. Make life take the mangos back! Get mad! I don’t want your damn mangos, what the hell am I supposed to do with these? Demand to see life’s manager!