Thank you all for your helpful suggestions.I realized that translating from English instead of the other way around is certainly a better way to approach this.Using ContentTranslation seems the best option, even though it currently does not contain support for auto translating the en/cs language pair.It is important to me to be able to see somebody else's unfinished translation and as far as I know, ContentTranslation does not support that yet. Is this feature planned?
I know the tool. I was one of the people who campaigned for having it enabled on cs.Wikipedia ;)
On that occasion I made a comparison table for all available translation tools for WIkipedia I know of (Duolingo, Google Translate Toolkit, ContentTranslation) and CT is a clear winner. Duolingo has problematic ToS and drops formatting and references, Google Translate for WIkipedia is not being actively worked on and drops some formatting and references. I guess as the developers you know all about that ;)