OK, briefly, because I don't want this to get out of hand.
1. "Patronising" means "talking down to people". This you certainly did. To quote you: "And please, read your posts before you submit them. Make sure they are grammatically correct and that they make sense." If this is not talking down to someone then I don't know what is.
2. You didn't bother to read up about the country of origin of the writer before replying. To quote you again: "I can certainly understand if english is not your native
language(not sure if it is), but what you wrote is beyond non-native inexperience"
In the writers stats it is clearly stated that he is from France.
I am not sure what you mean "about the current state of the EU". People from France speak french, people from Germany speak german, just as they always have. This guy is making an effort to write in a - for him - foreign language. Rather than welcoming him and trying to help him you wrote a rude reply. Now, let's take a look at your own writing skills - and I take it that English is your first language:
"My post, in addition to first answering
his question, was to point out that what he posted was ugly in syntax, spelling, and
grammer, to the point of being confusing. And that if he wished people to respond to
him that it would help to clean it up."
There should be no comma before the "and" in your first sentence.
"grammer" is spelled incorrectly. "grammar" is the correct spelling.
The fragment "if he wished people to respond to him" should be enclosed by commata however. in addition, the second "that" in the same sentence is not needed and doesn't make sense.
I could carry on, but that would be nitpicking. All I am saying is, be polite to people who make an effort to communicate with you in a language that is not their own. Especially as you appear to be sitting in a glasshouse yourself.
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