That is also what I put. I don't see how there would be an "on" in this sentence as no such spanish word appears.
for something that happens "on" a day in English, Spanish uses the definitive article (el or los), which sounds weird to us, but we probably sound weird to them. :-)
It's just the way their language works. It's not always a one-to-one English translation.
I don't think "On Sunday we do not have plans" is typical English usage. The correct usage is "for Sunday." It is a difference of emphasis,but is meaningful. The issue is 1) when is it that you do not have plans and 2) what to the plans concern. " On Sunday we do not have plans." suggests that Sunday is when we do not have plans and does not say anything about what the plans are for. "For Sunday" indicates that we currently do not have plans relating to Sunday.
"We don't have plans this Sunday." is a similar meaning, but it's not what it says in Spanish. That would be a different a phrasing. (I think "Este domingo"?) If you think about the English, it's two different sentences, so in Spanish is it too: "We don't have plans on Sunday" and "We don't have plans this Sunday." Two different sentences like in Spanish.
If I say "This Sunday" or "on Sunday" they both refer to this coming Sunday and no other. To me, they both have the same meaning.
Can I say "On THE Sunday we do not have plans"? I know that this is not a typical way to say it in english, but it can refer to a specific Sunday?
This would be a very unusual situation grammatically, but not completely unheard of:
"I'm out of town right now, but I'll give you a call on the Monday after I return."
"On the Sunday of my goddaughter's baptism, I planted a tree in her honour."
Notice how there must be more information to specify (" ... after I return" and " ... of my goddaughter's baptism.")
In spanish, the days of the week usually take the definite article. In english, we tend to use 'on' before the day of the week. In spanish, 'en' is not required.
" Except in constructions where the day of the week follows a form of ser (a verb for "to be"), as in hoy es martes (today is Tuesday), the article is needed. Vamos a la escuela los lunes. (We go to school on Mondays.) El tren sale el miércoles. (The train leaves on Wednesday.)"
I used 'the sunday' also - it is not incorrect to do so in English, e.g.: on the Saturday we want to go to the park but on the Sunday we have no plans... I'm still not clear, despite the posts here, why this is incorrect in Spanish...
Can plans also mean like Death Star plans, or plans to the secret bunker? So blueprints?
Another one that is not political. Duo should check their items occasionally...