Go to Settings > Reading
It is mandatory to translate the static front page in all languages. If you choose a page not translated in all languages, you will get an error message and your choice will not be validated.
Choose one of the page you have just created (the language doesn’t matter). This “Front page” option gives you the access to a new option under Languages > Settings > URL modifications:
If you check this option, your Home page url will look like:
And the other one below will not exist anymore (it will send an error 404):