An additional "source" could be this online, browser-based TDE game site : http://www.tde-games.com/
"Conspiracy At Ferdok" is a side-story of Drakensang 1, part two of this Adventure (which is called "Death Trail", I think) is commercial.
And - yes, these are official games. Chromatrix is the TDE license holder for all video games based on the TDE rule set.
The only drawback is, that these browser-based games play rather like text adventures. Almost no graphics at all, but you'll get another insight into Aventuria.
- From Crystal's DSA-Foren : The required points for levelling up : As you can see, the German and the English-language games have different values there : http://nlt-hilfe.crystals-dsa-foren.de/page.php?211
As it turned out, there seem to exist different language versions for ROA games as well. Someone in the forums of Crystal reported buying a Spanish-language version. Moby Games lists titles for other languages as well.