"Is tomorrow Monday?"
Translation:¿Mañana es lunes?
This is a great page for understanding when to use the definitive article that someone was kind enough to post on another thread. Hope it helps. https://www.spanishdict.com/guide/using-the-definite-article-in-spanish
In Spanish we don't rearrange "is" to the front of the sentence when we have a question. It'll always be like "He is from Mexico?" or "It is poisoned?".
It could be because "es" means "it/he/she is", so saying something like "Es e'l me'xicano?" would translate to "He is he mexican?", which sounds really weird.
In Russian we ask things similarly. But we don't have words of "is" or "the" there, so I don't think we have much of a choice. So instead of saying "Is the cat bad?" we just ask "Cat bad?"
I hope I was able to clear at least something up.
Here is an explanation on caps: https://www.spanishdict.com/guide/capitalization-in-spanish