How do you say estoy asi asi in English?

You start by not saying "Estoy asi, asi" in the first place. It means "I'm that way, that way". It's a mistake made by Spanish students. Assuming you want to say "I'm so-so." In Spanish you would say, "Estoy mas o menos" or "Estoy regular".

"Asi" means "like that" or "that way". You could say, "Soy asi" meaning "I'm like that" or "I'm that way" referring to some character trait of yours. You could also say "Estoy asi" meaning, again, "I'm that way" but referring to how you are positioned or some condition you are in.