Translate
Translate Theme
It's theme translation, your site just can be displayed on 1 language, we don't support multiple languages for now.
You can add your language in Admin -> Translations -> Locales.
After adding your language, you can go to Admin -> Translations -> Theme translations to translate theme to your language:
When you done, click on the Save button on the bottom of page to publish translation.
Translate Admin panel
If you want to translate admin panel too, you can translate it in Admin -> Translations -> Admin translations.