Steps to reproduce: create a new WP instance in spanish, install and activate the Parabola theme and go to the main page of the site. The accents and other special characters not in english (i.e. “á”, “é”, “í”, “ó”, “ú”, “ñ”) are rendered in a different font (by default a serif font, even though the default for Parabola is Open Sans).
Open Sans includes those characters, but the version bundled with the theme doesn’t. Using the “load a font from Google feature” works flawlessly, but it should be included by default, or at least show a warning to users.
Most of the bundled fonts include the latin-base characters set. If you need characters that are part of the extended sets I suggest using the integrated Google fonts functionality or loading and embedding your own fonts on the site.