WPML lets you create virtual directories for all languages, including the default language. These are not real physical directories on the server’s drive, but virtual directories that only appear in URLs.
With language folders for all languages, your site’s structure can look like:
To enable this, go to WPML->Languages and scroll down to the Language URL format section.
First, you should select the ‘Use directory for default language‘ option. Then, enable the directory for the default language.
Once you’ve selected this option, you will need to choose what goes into your site’s root URL. For the root URL, you can choose between a WordPress page or an HTML file.
When you choose an HTML file, you need to provide its path. If the path starts with a slash ‘/’, it will be an absolute path on the server. Otherwise, it’s relative to the WordPress directory. You can upload that HTML file using an FTP program, placing it under your site’s ‘wordpress’ directory.