WPML is the most complete and powerful translations plugin for WordPress. You can use other plugins but WPML will save you tons of time and will give you more flexibility and quality. WPTF is already integrated and tested with this plugin.
WPML is not free, you must buy it for 29$, but WPML will let you translate your website faster and better than with any other plugin, and you know, time is money. Remember that if you need to translate all the theme and plugin strings you need WPML String Translations available only for Multilingual CMS of $79.