"I see you through the window."
Translation:Widzę was przez okno.
'Cię widzę przez okno' was counted as wrong. Is this an unnatural or wrong sentence? Or is this Duo just being Duo?
At the beginning of the sentence you should use an accented version of the pronoun so it would be "Ciebie widzę przez okno". And as it follows from the name you shouldn't use it if you don't really need it because this sentence is much more emphatic than "Widzę cię przez okno".
"ciebie" gives more emphasis, so it would be like "I see YOU through the window", that sounds a bit strange.