I tried that and it told me it sounds "awkward" in English :P
Here are some reputable sources discussing it: https://www.youtube.com/watch?v=ny18k07yMSI https://www.oxforddictionaries.com/definition/english/personal-pronoun#personal-pronoun__5
Todavía recuerdo un cómic que tenía de pequeño dónde el bueno preguntaba "quién eres" y entonces el malo se quitaba el casco y se veía que era idéntico al bueno, y decía: "yo soy tú".
Ni idea del significado porque no tenía ningún otro tebeo de la colección, pero aquello me dejó intrigado hasta el día de hoy.
You are incorrect. The copula to be has no accusative object. It is equivalent to the sign =. A is B, or A=B. Correct is, actually, both. And as such, it should also accept this version. How can "This" be nominative and "me" be accusative, if both is the same, pragmatically. Object does not mean any word following the verb, but is a complement for a full verb. To be is not a full verb, nor does ist function as a predicate here.
On some of the other languages, there are "accented letter" buttons underneath the box one types in. They tend to accept unaccented answers, though. One beef I have about this one is that there is no way to listen to the spoken prompts slowly, as there is in all but one of the other languages I've been learning on here.
I thought this would translate to: "You are mine." I'm not sure if that would be correct or not. Just from reading it though, that's what I thought. I know in this context someone wouldn't say such a thing. I would say: "em là anh" to a significant other of mine, but not necessarily to a person I'm using this language with. Just some thoughts.