First of all, before any kind of SEO, what you need in the first place is high quality content in every language. The kind of content users want to see and people may link to because it is useful and it adds something valuable to the World. In the second place, your site must be optimized for the people that use it, not for search engines. Search engines like Google do a nice job of listing first the best content for users to read.

That said, there are some tips that may help your multilingual Drupal site, that is plenty of high quality content and optimized for users in the first place, work better with search engines and help people find it -provided it is what they're looking for-. Most of this is valid for Drupal, Wordpress or whatever CMS you use, but the tools I am talking about are Drupal specific, which are the ones I've been building for some years...

I am the author and main maintainer of Internationalization module which is the one powering almost every multilingual Drupal site out there.

• SEO
• Drupal
• Multilingual Drupal