Games can use all manner of text encoding, or even not have text encoding and instead just have pictures with text in (a lot of puzzle games do this). Being a modern console the Wii is also no stranger to a full on text engine with all sorts of extras, though I would not assume this is the case until such a time as you actually see it happen.
Figuring out an encoding is considered the first thing you get to learn to do in the text hacking part of ROM hacking. I do not have any Spanish tutorials right now, or any Spanish ROM hacking communities (I have many for other languages but seemingly not Spanish right now) but
http://gbatemp.net/threads/gbatemp-rom-hacking-documentation-project-rewritten-for-2012.73394/ and
http://www.romhacking.net/start/ work for English. A quick search for Spanish ROM hacking communities does not get me far (
http://foro.romhackhispano.org/index.php might have something as might
http://romxhack.esforos.com/portal.php and there is the general site
http://www.elotrolado.net/foro_nds-scene_130 which could do something), there are several very good ROM hackers that have Spanish as their first language that frequent here and other hacking communities that might know more here though.
For a nice example of a complex engine seen in a wii game then
http://blog.delroth.net/2011/06/reverse-engineering-a-wii-game-script-interpreter-part-1/ . Again though most text hacking is far simpler than that.