As I commented earlier, the purpose of this modification was intended to avoid a 404 error when non-existent CSS files are loaded, since the most locales including en-US don't have a locale specific CSS.

Does this work on stage and production?
```conf
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^/media/css/l10n/(\w{2,3}(?:-\w{2})?/)/intl\.css$ /media/css/l10n/blank.css [L]
```