I have decided to go to an Englisch Language school in Ireland and finally decided on the final destination Cork. Could anyone comment on ACET school or Cork Language Institute?
ACET has a very good when it comes to its atmosphere and teachers. If you improve quickly, you get moved up into a higher course.
I can't say much about the Cork Language Institute as I am not familiar with them.

Some other schools you could have a look at which are situated in Cork are:
Cork English World or Study & Live in your Teacher's Home. Google them for more information.