Is it a correct English to say so true?

"So true" is a common phrase in spoken English, but it's not grammatically correct in formal writing.

Here's why:

* "So" as an intensifier: "So" is often used to emphasize an adjective or adverb, like "so happy" or "so quickly." In this case, it's acting as an intensifier.

* "True" as an adjective: "True" describes something that is accurate or factual.

While "so true" sounds natural in conversation, it's a bit informal. Here are some more grammatically correct ways to express the same idea:

* "That's true."

* "You're absolutely right."

* "I agree completely."

* "That's a very accurate observation."

So, whether it's "correct" depends on the context. In casual conversation, "so true" is perfectly acceptable. In formal writing, it's better to choose a more grammatically correct option.