Hi everyone, 

I tried the search function, but couldn't find anything. Is it possible, that the research to colonize barren planets is not implemented, yet?

You're right in guessing that. When you zoom in onto a system and mouse over a planet, it should show you what technology you need to colonize that planet. If the technology it tells you is "TechnologyUnknown", then that technology hasn't been implemented in the game yet.

For now, you can't colonize barren, gas and lava planets.

Here you go.

https://www.games2gether.com/endless-space-2/forum/75-modding/thread/21382-mod-unlocking-planets-for-colonising