Can't access to the admin anymore

yes, I look from here to see what it does by clean approach.

done. (I’ll add an empty index html file, i don’t like this view of the directory)

popandsoda.com

so far so good, no more additions no /en and no /fr

But popandsoda.com/blog/ gives – popandsoda.com/fr/blog/ and the page:

Not Found
The requested URL /fr/blog/ was not found on this server.

Now only place the index.php with adjustment back in the root (not the .htaccess file)

ok.
I’ve placed the original index.php file, which contains :
require(‘./blog/wp-blog-header.php’);
(notice the dot before /blog/)

(notice the dot before /blog/)

Remove the dot…

dot removed:
require(‘/blog/wp-blog-header.php’);

is there another file called index?

yes, empty index.html that I have just added (otherwise anyone can access the directory)

Oops! Just removed the html index, sorry…

please rename this to index-old.html, on your server this file is given priority

I’ve removed the html index actually…

Do I replace the html index back and rename it?

index.php is there with this?

/**
 * Front to the WordPress application. This file doesn't do anything, but loads
 * wp-blog-header.php which does and tells WordPress to load the theme.
 *
 * @package WordPress
 */

/**
 * Tells WordPress to load the WordPress theme and output it.
 *
 * @var bool
 */
define('WP_USE_THEMES', true);

/** Loads the WordPress Environment and Template */
require( dirname( __FILE__ ) . '/blog/wp-blog-header.php' );

I get a white screen.

yes, without the dot :

<?php
/**
 * Front to the WordPress application. This file doesn't do anything, but loads
 * wp-blog-header.php which does and tells WordPress to load the theme.
 *
 * @package WordPress
 */

/**
 * Tells WordPress to load the WordPress theme and output it.
 *
 * @var bool
 */
define('WP_USE_THEMES', true);

/** Loads the WordPress Environment and Template */
require('/blog/wp-blog-header.php');

Now I’m wondering if the ‘<?php’ is needed?

aaaah, the require is different!