How to write in another language

Hello!

I have to write many texts for my university, however, not always they are on the same language. I usually write in my native language (Brazilian Portuguese, which is my System Language), but I need to write texts in English too.

My problem is: everytime I write in English, EVERY WORD is underlined in red. So, how can I change the language I'm using on Pages (without actually changing the entire OS X's language -- or Pages' UI)? Is it possible, like it used to be in iWork '09?

Thanks in advance.

Matheus.