I have a blogspot.com blog where right side reads in english "previous posts" "archive", but the "about" part is in spanish (perhaps because I'm on latinamerica). And some of my posts are in english, but others in spanish and portuguese, since the blog is about a specific region of tourist interest in latinamerica.
I'm mostly intersted in portuguese now, since they seem to be the most appropiate public for the content.

So I really have a mix of languages and I'd like to migrate to portuguese. How do I do that on Blogger?

I can translate my old posts or just write new ones on portuguese, but what else?