In the /includes/languages - you should have english.php, french.php, german.php, italian.php, & spanish.php

You then also need folders:
/includes/languages/english
/includes/languages/french
/includes/languages/german
/includes/languages/italian
/includes/languages/spanish

and in these folders, respectively, any files that have been translated i.e.
header.php
create_account.php
and so on

along with language specific custom template folders & contents

If you have a custom template folder in /includes/english/my_template
You need this replicated for each language