How do I redirect a multi language site to a default language page?

Question

I have this:

http://example.com/EN/index.php - english version

http://example.com/PT/index.php - portuguese version

What I want: http://example.com/ to be taken to the portuguse page by default.

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I've also been thinking on having the portuguese page on the root and english in the EN/ directory. is this better for SEO?