Even if it is wrong in Turkish, the English sentence should be written according to English language 'norms'.
In Arabic, 'me' or 'I' come before 'you'. So it is the 'norm' to write "أنا وأنت سنذهب إلى السوق" (literally: I and you will go to the market.)
However, when the above (Arabic) sentence gets translated into English, it would be written: You and I will go to the market.
In translation, one should follow the 'norms' of the language used. You are communicating meaning across languages, not sentence structure.
i do also! but if wrong i think it is only to show that you understand that (here) kedim does not mean 'you'.
when learning the order counts so we have to directly translate the order. it may mean you & my cat but it says my cat & you. if that makes sense :)
maybe it's written with personal possession first as to many they think of themself first
"Sadece kedim ve sen." Translation: Only my cat and you.
why it is wrong to say my cat and you only instead of only my cat and you?
Sadece - (adverb) - "Only"- "Just."
The question asked in Turkish has the adverb before the (subjects) The first subject has the possessive suffix "-im." - "My cat" & you. The adverb modifies the first subject - the cat.
I understand your English answer & it appears to be correct in spoken English.
Sorry - that's the limit of my explanation. We need a second opinion?
(Native English speaker) In answer to your original question, why is "My cat and you only" not accepted as a correct answer: I suspect that Duo just has not added it. In a short phrase, either would work as correct English. But please note, this is not a full sentence. If I ask, "Who likes fish?" you could answer, "Only my cat and you" or you could answer "My cat and you only." But in a full sentence answer, you would say "Only my cat and you like fish." If you said, "My cat and you only like fish" then you would mean that both you and my cat like nothing but fish, and there is nothing else you like to eat. (Also: In English natural speech we would be likely to say, "Only you and my cat," not "Only my cat and you." Clearly this is different in Turkish:)