Translate the content of your site with Google Translate... Not always correct, but the visitor knows what you want to say... The built in, multilanguage module in the core of Drupal 8 allows you to do the translations yourself. This is much better than GTranslate, but needs a lot of work..

Language icons

If you want a mulitilanguage site, you have to activate the language modules built in the core. You have than a block with the language choise. This module puts flags next to the languages automatically.

A multilingual site

In Drupal 7 you had the Localization update module (i10) and the Internationalization module (i18n) for building your multilingual site. Adding some flags with Language icons and done... In Drupal 8 everething except the flags are build in the core.