Difference between "already know" and "have already known"

Solution 1:

When we use the word already with the present perfect, we are usually referring to a completed action (which has present relevance):

• I have already cooked dinner.
• She has gone already.

But knowing cannot be regarded as a completed action in the same sense. It denotes a present or past state. So you cannot say:

• I have already known that they are getting married.
• I have already known how to speak Russian.

What you can say of course is:

• I have already heard that they are getting married.
• I have already learned how to speak Russian.

because hearing and learning can be regarded as completable actions.

And you can use already with the past simple to denote a state of knowledge that existed at some point in the past (and may or may not exist in the present):

• I already knew that they were getting married (before I read it in the newspaper).
• I already knew how to speak Russian (so I didn't need to do the course).

Unlike some languages English does not have two verbs to distinguish between a. knowing a person and b. knowing a fact or how to do something. With the former meaning it would be possible to say:

• I have already known many people like you and have learned not to trust them.