In order to create a multi-language Magento 2 store you need to add a new store view by going to Admin Panel > Stores > All Stores and pressing the Create Store View button.
Store View Information
1. Choose store the store-view will be linked to in Store select box.
2. In the Name field, you correspondingly set the name of the store-view.
3. Set the code of the store-view (it can be used in the URL).
3. Enable the store-view in Status select box.
Once you have finished with all the changes don't forget to press the Save Store View button.
Also, you can edit store-views, e.g. change the name of a store view. You can do this by clicking on store-view link and editing its fields easily, just like during the creation.
Set Locale (Set Language)
Once creating a new store view has been done, you have to set it's locale by going to Admin Panel > Stores > Configuration > Store View > [Store View Name].
In the General section find Locale Options and set a language for the store view.
Once you have finished with the store view locale configurations don't forget to press the Save Config button.
After all these actions you should reindex Magento 2 and clear the cache.