I have some good news for our Latin American summoners out there! Riot has begun it's alpha testing on the upcoming Latin American servers. These servers will be split into Latin America North and Latin America South and feature a full translated Spanish client and voice overs.
The Latin America North Alpha has already started, as evidenced by it's availability in the Regional settings of the launcher.
I would suggest making your way to the official League of Legends Latin America Facebook page if you seek more information about all this. There you'll also find all sorts of sample champion voices from noteworthy Latin American voice actors.
PS: If anyone else has any relevant information about this, feel free to share! I know this is exciting for many of you and I apologize all I have to go on is google translates of the announcements.