How can I add the Spanish ? to a permalink?

Hello.

I’m using the English-version of WP 3.8.1, but I still haven’t been able to figure out how to add ?, plus vowels with accents, to a Spanish-language post. WP keeps converting ? to n, and removing the accents to á, é, í, ó, and ú. How can I make this work? I want to do something like mysite.com/2014/03/ellos-hablan-inglés-francés-y-espa?ol (example).