In the many years that we have worked with WPML, we have been involved in hundreds of multilingual websites in more languages you and I can imagine.
Typically our work is related to setting up and configuring WPML and building custom language switchers, but it can also get much more complex with writing custom functions to adjust specific things or make incompatible themes and plugins work with WPML.
Another plugin that is gaining ground making websites multilingual is Polylang; we also offer our assistance and expertise with setting up and configuring this plugin and building custom language switchers.
A related and ever-growing market is to make eCommerce websites function in two or more languages and even different currencies.
WPML and WooCommerce have realised this early on and are the perfect partners to accomplish this.