It really, really depends on the school and the co-teachers. Most jobs for foreigners in the public school system involve teaching your regular lessons with 'co-teachers', but how this works out in reality is very hit and miss. At the one extreme you may have CTs who never come to class with you and on the other end you may have ones who plan a lesson and just use you as their puppet / human tape-recorder. More common is a CT that usually comes to class but then stands or sits at the back most of the time leaving the foreign teacher to lead everything.
In my experience all of the CTs I've with whom I've worked prefer me to plan everything and lead the lesson, and if there's anything I want them to explain or translate they much prefer that I give it to them in advance of the lesson. If it's for a lesson where for most of it I don't really need a CT I might cover the part I want to do with the CT near the beginning of the lesson, after which they can go back to the staff room if they have better things to do.
"I don't really see how effective the classes would be if the co-teacher translates everything."
You're bang on.
















