Multilingual / SEO capabilities

Hi,

I’m looking to start a word-press solution that will answer the following problems:

Multilingual
sitename.com/en/content1 /// sitename.com/es/content1 /// sitename.com//fr/content1

At first, the articles should be dynamically created using Google translate (I’ve seen plugins for this somewhere). Another requirement is that I will need to replace the dynamic content with correctly translated static content at a later date. So I will need to manually override the content pages for the relevant country.

The final requirement, is that the whole thing needs to be as good as possible when it comes to SEO. I’m essentially targeting many countries / regions.

What’s the best solution chaps?

Thanks in advance ??