"The dog does not see mice but cats."
Translation:Ten pes nevidí myši, ale kočky.
Ten pes nevidí myši, nýbrž kočky < this is what my correction gave me after mistyping (typed nebo instead of ale). If I use google translate (I have never seen nýbrž before) it says "instead of", but here we have "but". Kind of confusing, I knew the word I had mistaken, but then I read this and start to get confused.
Nýbrž is the same as ale here. Do not trust Google translate for Czech, I can't recommend it. For single words there are real dictionaries available (I use slovnik.cz).
There are other variants of ale which are even more exotic than nýbrž in dictionaries (like alébrž...) but you are unlikely to encounter them.