nginx: redirect when accept language is other than english

Question

I have a multi-lingual website and want the URL schema to work like

https://example.com/            -> Load english version
https://example.com/path        -> Load english version
https://example.com/es/         -> Load spanish version
https://example.com/es/path     -> Load spanish version

and using the nginx configuration

map $http_accept_language $accept_language {
    ~*^es es;
    ~*^en en;
}

server {
    server_name                  example.com;

    location /docs {
      alias                       /var/www/html/app-frontend/documentation/;
      try_files                   $uri$args $uri$args/ /docs/index.html;
    }

    # Fallback to default language if no preference defined by browser
    if ($accept_language ~ "^$") {
        set $accept_language "en";
    }

    # Redirect "/" to Angular application in the preferred language of the browser
    rewrite ^/$ /$accept_language/ permanent;

    # Everything under the Angular application is always redirected to Angular in the
    # correct language
    location / {
        alias /var/www/html/app-frontend/en-US/;
        index                     index.html;
        try_files                 $uri $uri/ /index.html = 404;
    }

    location /es/ {
        alias /var/www/html/app-frontend/es/;
        index                     index.html;
        try_files                 $uri $uri/ /index.html = 404;
    }
}

I want the nginx to redirect to language code if the detected language is not english. But the above configuration, redirects to /en/ when the language detected is english.

How can I point the root path (without language code) to the english version?

Tried moving rewrite statement inside if check as follows

if ($accept_language !~ "en") {
        rewrite ^/$ /$accept_language/ permanent;
}

# rewrite ^/$ /$accept_language/ permanent;

It works fine. But it looks like the configuration can be more optimized.