I'll answer my own question, in case anyone else is wondering.
You can't type accent marks manually, but accent marks do appear on some words in predictive text mode. When I changed the text mode from English to Spanish, I was expecting Spanish letters (é á ñ etc) to appear in the symbols menu. What it actually does is change the language of the predictive text. So you have to turn Spanish mode and predictive text mode both on, but even then, like I said before, the accents are only on some words (sí and cómo are nowhere to be found). So, that's it I guess.