The reaction of a casual but curious browser:
I've read somewhere
I think it a shame that people posting on this forum do not keep track of whatever it is they think they have 'read somewhere'.
I've tried using the internet to find out, but no luck.
I'll grant that it isn't practical to provide us with a detailed log of your web-search activities. Nonetheless, what have you found, and what's causing the confusion in you?
I did my own Google search on "booster seat requirements Germany" and came to the conclusion that, once again, spread of rumor, misunderstanding and other sorts of misinformation is common on the internet. Web forums, personal blogs and similar 'uncontrolled' information' sites score high on the guilty-as-charged factor.
And just in case my point isn't clear enough: the info is already out there. All I or anyone else can do is repeat it. Without a credibility check on we who post answers, you're not in any better position than you already are in.
Which makes it all the more useful if you could state with more precision what's confusing you and/or why you can't find the info.