There are at least three ways to achieve this:

• choose 'Send' on the Google Maps page and send the route as an email to yourself, then drag and drop the email body from the mail program into RouteConverter
• choose 'URL for this page' on the Google Maps page to display an URL for the current route, then drag and drop the URL into RouteConverter
• drag and drop the Google Maps URL from the Webbrowser into RouteConverter

To drop something into RouteConverter choose the right side of RouteConverter or the elevation profile in the bottom. The left side is used for the map which is an embedded web browser which cannot be used as a drop target.

RouteConverter is fully based on the Google Maps API and additionally uses Tile-Server from OpenStreetMap to display the map and the overlays for tracks, routes and waypoint lists.

Even if the map data is available offline - this is imaginable for OpenStreetMap maps - there would be gaps regarding the functionality: the routing for routes, the complementing of positions with elevation and place information, finding places, adding positions and the RouteCatalog depend on webservices, too.

I'd be willing to help, if you'd like to spend time, to make the maps available offline.