Here is the full list of all 61 Hidden Cats in Berlin achievements. It takes around 1-2 hours to unlock all of the achievements on Windows.
The Underground Party Completed
You Found 800 Cats
Tiergartent Completed
You Found 700 Cats
Metzgerei Completed
Hauptbahnhof Completed
You Found 600 Cats
Brauhaus Completed
You Found 500 Cats
Berlin Wall Completed
You Found 400 Cats
Backerei Completed
Found All Cats Advanced
Finish with no Hints Advanced
You Found Einstein's Cat
You Found 300 Cats
You Found Irena
You Found Wurst Cat
You Found Luke
You Found Capuccino
Berlin Wall Discovered
You Found Bethoven's Cat
You Found 250 Cats
You Found Grumpy Cat
You Found Gothic Punk Cat
You Found Darvin
You Found 200 Cats
You Found Goethe's Cat
Oberbaumbrucke Discovered
Berlin Tiergarten Discovered
Brandenburg Gate Discovered
You Found 150 Cats
Pergamon Museum Discovered
You Found Bichin
You Found Clóvis
Hauptbanhoff Discovered
TV Tower Discovered
Postdamn Platz Discovered
Finish with no Hints Normal
Found All Cats Normal
You Found 110 Cats
You Found 100 Cats
You Found 95 Cats
You Found 90 Cats
You Found 85 Cats
You Found 80 Cats
You Found 75 Cats
You Found 70 Cats
You Found 65 Cats
You Found 60 Cats
You Found 55 Cats
You Found 50 Cats
You Found 45 Cats
You Found 40 Cats
You Found 35 Cats
You Found 30 Cats
You Found 25 Cats
You Found 20 Cats
You Found 15 Cats
You Found 10 Cats
You Found 5 Cats