Magento Open Source 2.2.x
Adding a Language

Most of the text that appears to be hard-coded on pages throughout your store can be instantly changed to a different language by changing the localeA set of configurations that defines the user’s language, country, tax rate, and other settings. of the view. Changing the locale doesn’t actually translate the text word-for-word, but simply references a different translation table that provides the interface text that is used throughout the store. The text that can be changed includes navigational titles, labels, buttons, and links such as “My Cart” and “My Account.” You can also use the Inline Translation tool to touch up text in the interface.

Language packs can be found under "Translations & Localization" on Magento Marketplace. New extensions are continually added to Marketplace, so check back often!