I think that "on" is unnecessary in this particular sentence although I accept that other examples are better/need the "on".
Very normal in British English. It is an immediate identifier of American to say "I do it Saturdays" - sounds terrible to Brit ears. We use the "on" for a specific day or implicitly every such day. We know your usage but clearly you don't know ours!
It may sound terrible to a British ear, but both "Englishes" are valid. Duolingo should accept both answers or create two different platforms for American English and British English.
One of the inevitable consequences of people learning another language is that they broaden their outlook. Why do you want to go backwards and be exclusive rather than inclusive? By the way, all of the people I know use "on Monday."
My ears have been British from the day I was born over 70 years ago, so do be careful with labels. 'I do it Saturdays' does not sound terrible to my ears.
We're not comparing England English to American English. We're comparing American English to Spanish.
"Work Saturdays" is colloquial spoken English, but this is not formal English.
I thought that to express this kind of need we would say, "Tengo que trabajar los sabados."
No context was given. This sentence expresses a 'need' to work on Saturdays. (Maybe the person would otherwise be bored for example.) You are right that "tener que" means "to have to" work. As in "must"
Im not to swift ....but There is no indication of ....on ...in the phrase....and if there was...it would be used for a single saturdays
It is colloquial to add "on" in English when saying "I need to work on Saturday." Similarly, it is colloquial Spanish not to say "on."
This is saying I have to work on all Saturdays. How does one say "I have to work on Saturday" i.e. the next one or the one we're talking about?
Necesito trabajar el sabado. Or, Tengo que trabajar el sabado. Hope this helps John.
Whoever created this sentence's correct answer simply did not realize this is also acceptable.