Yes, you capitalize Spanish because it is a language and culture.
It is not necessary to capitalize the word "yo".
Yes.
You underline or italicize them.
The Spanish word for October is octubre. (Many languages do not capitalize month names.)
You always capitalize proper names, and Spanish is a proper name for someone or something from Spain.
Only capitalize I (yo) at the beginning of a sentence.
If your using it as your first word in your sentence... Yes you do, but if yoour not no.
The word for "god" in Spanish is "dios." If you are talking about the Christian God, then you capitalize the D of "Dios." It is pronounced "dee-OSE."
You should capitalize a language when it is the name of the language or when referring to it as a proper noun, but not when used as a common noun. For example, "I am learning Spanish" (correct) vs. "I am learning how to speak spanish" (incorrect).
Spanish should be capitalized but olives shouldn't be.
In Spanish, months are not capitalized unless they are used at the beginning of a sentence or part of a proper noun.
prestado, in the context of "gave a loan." If you meant to capitalize, Lent, then it would be Cuaresma.