I have just added “Groupchats for Kontalk?” to the FAQ page. Because the german FAQ page is linked in this article. I hope it’s OK 
I tried to comment on their Disqus, but they don’t accept comments “as guest”… 
I’ll do it here then:
Quick translation: Open source is only secure, if you review the code yourself (and don’t rely on third parties), compile the source code and all dependencies (libraries) yourself and run the server yourself.
That is probably correct, but many can’t do all of this themselves. Who can you trust, if you don’t even trust F-Droid?
F-Droid is a non-profit volunteer project. Although every effort is made to ensure that everything in the repository is safe to install, you use it AT YOUR OWN RISK. Wherever possible, applications in the repository are built from source, and that source code is checked for potential security or privacy issues. This checking is far from exhaustive though, and there are no guarantees.
Source
Done 
Why must a post be long in this forum at least 20 signs?
OK now it’s long enough
That’s a threshold that the admins can modify. It’s basically there to prevent posts like:
Just a joke! However, one could argue that a simple 
is enough for one-word approvals. (I myself sometimes just write things like “Done”. At the Fairphone Forum we have lowered the threshold to 10 characters.) Or maybe the threshold exists to make you think of more to write, like
Done, Sir Principal Master Dev, Sir!
Es muy importante que Kontalk sea software libre y que los fuentes se puedan conocer (a pesar de que yo no entiendo nada de código fuente). Telegram por ejemplo, aparentemente es libre, pero tiene codigo fuente en el servidor que NO es libre, por eso considero que es mejor usar Kontalk… a pesar de que Kontalk puede que no tenga tantas funcionalidades.