I am exploring dispatcher rewrite rules and i'm fairly new to this.
Here with the rewrite rule RewriteRule ^/?$ en.html you have achieved the redirection on only dispatcher now there is one step which is left i.e. on publish environment you need to go to /system/console/configMgr and open Apache Sling Resource Resolver Factory(org.apache.sling.jcr.resource.internal.JcrResourceResolverFactoryImpl) and add in URL Mapping /content/we-retail/us/:/. Do not remove the already existing entry /:/ add after that. This is needed so that internally page can be mapped to correct resource.