Redirect from example.com to example.com/it first then to some proxy app.

This will preserve any URI after example.com, for example

example.com/images/image1.png

will become

example.com/it/images/image1.png

The option with using return directive is faster.

upstream ups {
    server 127.0.0.1:3010 fail_timeout=10s max_fails=3;
}
 
server {
    listen 80;
    server_name example.com;
 
    access_log /var/log/nginx/ups_access.log;
    error_log /var/log/nginx/ups_error.log notice;
 
    location / {    
        return 301 /it$request_uri;
 
        # alternative using rewrite
        # rewrite ^/?(.*?)$ http://$host/it/$1 break;
        # rewrite_log on;
    }
 
 
    location /it {
        proxy_pass http://ups;
        proxy_set_header Host $host;
    }
}

You can check the rewrite messages in specified error log.

server conf:

   location / {
        return 301 /$lang/$request_uri;     
    }
 
    location /it {
        proxy_pass http://ups;
        proxy_set_header Host $host;
    }
 
    location /en {
        proxy_pass http://127.0.0.1:3000/;
        proxy_set_header Host $host;
    }

In http context add the mapping for $lang, e.g.

http {
        ...
 
        map $http_accept_language $lang {
                default en;
                ~it it;
                ~es es;
                ~fr fr;
        }
 
        ...
 
}

• Debian 11
• nginx/1.23.1

• Nginx troubleshooting
• Redirect to another site from query parameter in nginx

• https://stackoverflow.com/questions/35949123/nginx-rewrite-root-url-with-language-suffix
• https://serverfault.com/questions/407028/nginx-rewrite-or-return-for-redirection