Polylang

With Polylang fully integrated to WordPress and using only its built-in core features (taxonomies), keep steady performances on your site and create a multilingual site featuring from just one extra language to 10 or more depending on your needs. There is no limit in the number of languages added and WordPress’ language packs are automatically downloaded when ready.

Depending on the type of site you have built or are planning to build, a combination of plugins from the list below might be of interest.
All plugins include a wizard allowing to install them in just a few clicks.