They can be defined, but nobody does so explicitly. Consider the classic example of the order of adjectives.
You can have a big brown bag, but if you have a brown big bag, something sounds wrong. You can have an excellent blueberry muffin, but not a blueberry excellent muffin. You can meet your 27-year-old Ukrainian friend, but not your Ukrainian 27-year-old friend.
Unless you majored in linguistics or learned English as a second language, you probably never once even thought about the rules of adjective order in English (and in other languages the rules are often different!). But you know them, follow them, and people who don't follow them don't sound right to native English speakers.
I knew you were gonna mention this one and I don't think it really qualifies as it's not really an unspoken rule, it's the pretty well known and strictly defined adjective ranking order.
It is perfectly valid indeed. This person's main complaint is that Germans, who have enough English in their society that that one might even expect dialects to form, are not putting enough effort into disguising themselves as native English speakers. I'd call it 50/50 that the people who built this product speak English at work.
This is like ranting about Microsoft's website using American spelling when clearly they're selling to British people as well, only worse. This is pretty short-sighted. To OC, please keep thoughts like this to yourself. I hope you're not doing this for all the different stylistic usages of English out there, otherwise things are not looking good for literally any Australian business.
This sort of "feels wrong" non-native yet grammatically correct use of language is precisely the kind of thing that would be fine on an internal doc where comprehension is the name of the game, but falls flat on its face on external communications where a more fuzzy "trust" is trying to be engendered.
Or to put it more abruptly - if the release marketing is so low effort they haven't even bothered to get a professional translation, it suggests the same care and attention may have been lavished on the product.
"You need X?" works in a casual setting. But IMHO it looks pretty out of place in a more formal sentence like this with so many fancy nouns.