Native Brit English speaker here. Seems to me that you could use "Saturdays" or "Saturday" here and both would be correct. Both could mean "Saturdays in general" as in the Italian. Does DL accept both?
Yeah that's frustrating and definitely is more of a UK format. Such as when we say "Saturday next".
I wrote "school finishes on Saturday before noon". Wrong!
Point is: Duo needs to embrace more variations!