Does the sentence below in English seem grammatically correct to you?

[Anonymous]

I wish that other girl’s boyfriend was mine instead

[AviatorTom]

Except for the missing period (full stop) at the end, it is grammatically correct.

But its meaning could be ambiguous. If you put the word "the" between "that" and "other", the meaning changes...

"I wish that the other girl’s boyfriend was mine instead."

[Drew-1990]

Looks fine to me, why do you ask is English not your first language?

[Abbycado]

Yep. Grammatically, it is fine. No period at the end though.

[abc3643]

Yes, it seems fine and makes complete sense.

[serious]

Yes it is correct.