Nginx – In Nginx config, how to limit regex matching

1. In rewrite you match against URL's path part only. Which means, $1 will not contain the query string.
2. By default, Nginx appends original query string to the rewrite replacement.

So, it should be safe to write

rewrite ^(.*)$ $1?locale=de-de break;

In the case you do not want Nginx to append the original query string, simply specify ? in the end of replacement URL:

rewrite ^(.*)$ $1?locale=de-de? break;

I haven't tried this myself, but it should work. Add this inside your server {} block:

location / {
    if ($args !~ ^$) {
        rewrite ^ $request_uri? permanent;
    }
}

What this block actually does:

location / tells nginx to apply these directives to all requests matching root directory and subdirectories.

if ($args !~ ^$) checks if the URI contains any query parameters with regular expression.

rewrite ^ $request_uri? permanent; makes the redirect to the desired URI without any query parameters. The ? at the end of $request_uri tells nginx to strip query parameters from the redirect URL.