Convert display language to subfolder with htaccess - .htaccess

Question

For a website I have locally, I need to set the display language as if it were a subfolder, using an htaccess file.
For example, if I choose to display the site in German, instead of displaying it like this => local_ip/test/index.php?lang=de, I would like it to be displayed like this => local_ip/test/de/ .
Also, if I type in the url without setting the language, I would like htaccess to automatically redirect to the German language, from so => local_ip/test/tour/mountain/ to so => local_ip/test/de/tour/mountain .
My current htaccess file is structured as follows:
DirectoryIndex index.php
RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
RewriteCond %{QUERY_STRING} ^t=(.+?)
RewriteRule ^city/(.+?)/?$ city.php?url=$1&t=%1 [NC,L]
RewriteCond %{QUERY_STRING} ^p=([0-9]+)
RewriteRule ^city/(.+?)/?$ city.php?url=$1&p=%1 [NC,L]
RewriteCond %{QUERY_STRING} ^t=(.+?)&p=([0-9]+)
RewriteRule ^city/(.+?)/?$ city.php?url=$1&t=%1&p=%2 [NC,L]
RewriteCond %{QUERY_STRING} ^c=true
RewriteRule ^city/(.+?)/?$ city.php?url=$1&c=true [NC,L]
RewriteRule ^city/(.+?)$ city.php?url=$1 [NC,L]
RewriteRule ^tour/(.+?)$ tour.php?url=$1 [NC,L]
SOLVED
After several attempts and after reading several support requests posted in this community, I found a way to make the system recognise all the other rules as well. All I had to do was put them before the last rule provided by the user who supported me. Here is the final code.
RewriteEngine On
RewriteCond %{ENV:REDIRECT_STATUS} 200
RewriteRule ^ - [L]
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
RewriteCond %{REQUEST_URI} !/de/ [NC]
RewriteRule (.*) /test/de/$1 [R,L]
RewriteRule ^de/$ /test/index.php?lang=de [L]
RewriteCond %{QUERY_STRING} ^t=(.+?)
RewriteRule city/(.+?)/?$ city.php?url=$1&t=%1&lang=de [NC,L]
RewriteCond %{QUERY_STRING} ^p=([0-9]+)
RewriteRule city/(.+?)/?$ city.php?url=$1&p=%1&lang=de [NC,L]
RewriteCond %{QUERY_STRING} ^t=(.+?)&p=([0-9]+)
RewriteRule city/(.+?)/?$ city.php?url=$1&t=%1&p=%2&lang=de [NC,L]
RewriteCond %{QUERY_STRING} ^c=true
RewriteRule city/(.+?)/?$ city.php?url=$1&c=true&lang=de [NC,L]
RewriteRule city/(.+?)$ city.php?url=$1&lang=de [NC,L]
RewriteRule tour/(.+?)$ tour.php?url=$1&lang=de [NC,L]
RewriteRule ^de/(.*)$ /test/$1 [L]

Answer 1

You can use the following :
RewriteEngine on
#redirect URLs to include /de
#RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_URI} !/de/ [NC]
RewriteRule (.*) /test/de/$1 [R,L]
# /test/index.php?lang=de to /test/de
RewriteRule ^de/$ /test/index.php?lang=de [END]
RewriteRule ^de/(.+)$ /test/$1 [END]