Which sentence is correct?
"I am the one who speak (or speaks ??) English." ?
In constructions which have the form I am + noun or noun phrase + who, the verb following who agrees with the noun (the antecedent of who) and is therefore always in the third person (singular or plural):
I am the sort of person who likes peace and quiet.
You are the fourth of my colleagues who's told me that ('s = has, agreeing with the fourth).
So in our example, one means person.