How to respond that you agree with, say, viewpoint? Such as "think so too". Any altrnatives?

Question

Answer

I would simply say "I agree" or "I agree with you". Wordier alternatives tend to be more formal without adding significant meaning.

Answer

Mona: I THINK THAT ENGLISH IS THE BEST LANGUAGE IN THE WORLD.
James: Me, too.
Alicia: So true!
George: Absolutely.
Nancy: That goes without saying.
Tom: I'm with you.
Patricia: Is there any doubt?

Answer

Art:

As Randy indicates, you can say;  "I concur".

I find that I express myself  as follows to show this idea.

"We are in agreement."
"You and I are in accord."
"You and I have obtained to a harmonious accord."
"Our thinking is parallel on this issue."
"We are not in disagreement."
"Our thinking is the same."
"That is an equivalent idea."
"We have equal conclusions."

Answer

There are an almost infinitive number of ways to express that idea. I agree,  I concur, ditto, likewise, same here, the same.