In most cases where multilingual is required, I end up using Drupal, but in this case I really needed a WordPress solution.
On WordPress.org you can find a lot of information about setting up a multilingual WordPress — http://codex.wordpress.org/Multilingual_WordPress
My initial idea was to opt for a “multi-site” solution so I started exploring Multilingual Press and Multisite Language Switcher.
I do like the workflow of this plugg-in, but the lack of support for custom types and the need to debug from the start, discouraged me to use his plugin.
Multisite Language Switcher
Probably the best concept as you can link content to other content types. But it requires a translated WordPress interface for every language (installing a .mo file) and it becomes rather cumbersome in case you have to manage a lot of content.
WPML – ($79)
Until now the best solution, although it’s not using a multi-site environment but offers the same user experience.