htaccess – Internal server error 500

On several moments users get a 500 internal server error after switching a language.
It seems that the .htaccess will be overwritten every time with a . /nl/index.php (L) directory.

I contact the developers from Translate press that they must fix this. But they are still searching for a solution. Locking the .htaccess by the provider is no solution because we have several admin and webshop manager users in our website who need to have the rights to write.

.htaccess:

<IfModule mod_rewrite.c>
  RewriteEngine On
  RewriteBase /projectname
  RewriteCond %{REQUEST_FILENAME} !-d
  RewriteCond %{REQUEST_FILENAME} !-f
  RewriteRule ^(.*)$ index.php?url=$1 (QSA,L)
</IfModule>
# BEGIN WordPress
# The directives (lines) between "BEGIN WordPress" and "END WordPress" are
# dynamically generated, and should only be modified via WordPress filters.
# Any changes to the directives between these markers will be overwritten.
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteRule .* - (E=HTTP_AUTHORIZATION:%{HTTP:Authorization})
RewriteBase /nl/
RewriteRule ^index.php$ - (L)
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /nl/index.php (L)
</IfModule>

# END WordPress 

Error log:
2021-07-19 06:56:31 UTC (apache)(core:error) (pid 48256) (client 77.162.111.90:58418) AH00124: Request for staging8.avonic.com:/home/u1178-1xbbjbxooutv/www/staging8.avonic.com/public_html exceeded the limit of 10 internal redirects due to probable configuration error. Use ‘LimitInternalRecursion’ to increase the limit if necessary. Use ‘LogLevel debug’ to get a backtrace., referer: https://staging8.avonic.com/nl/product/av-cm22-vcu/

Any idea how to fix this?