1/
I observed that are string type are defined with a collation as "latin1_swedish_ci" ?
So why this and is it the default ?

2/
How to define a table field from COOK to be declared in SQL as uniq ?

1/ What would you like ? UTF8 ? (just a question, i'm not arguing here)
2/ can't do it in cook, but simple to change.

1/ utf8 is a good choice by default I think.
2/ phpMyadmin can do it.

2/ Yes, but what happens if the user tries to input the same data again (just try it, for practicing purpose)

There is no default collation imposed by Cook.
It will create from the default collation of your database.
All my components tables are in UTF8, generated by Cook.



About UNIQUE :
It will be available in 2.0, and I think also with an Ajax facultative query directly in the validator

EDIT : It is not done yet, because of the sandbox restoring datas.
If you define an UNIQUE after having inserted datas, the system can crash on restoring, so I am currently building a restoring process that will add suffixes to the datas to keep them uniques, or to skip them when impossible to add a suffix (int, fk...)
Well it is not easy to go around all kind of possibilities that the user can create