Hilla Vaadin Router and optional named parameter with regexp pattern

Question

I am using Vaadin Hilla and like to define a route in my typescript frontend routes.ts with an optional named parameter for the language which should be optional like :lang?. The optional language parameter should follow a reg-exp pattern for two alphabetical character \w{2}.

So the route should match:

• /categoryA/categortyB/...
• /en/categoryA/categoryB/...
• /de/categoryA/categoryB/...

I tried multiple multiple variants for the path, but I could not make the named parameter :lang optional when I use a regexp pattern like :lang(\\w{2})? or :lang(\\w{2}?) or :lang((\\w{2})?). The only thing which seems to work is :lang?

Any suggestions?

import type { Commands, Context, Route } from '@vaadin/router';
...
export const routes: Route[] = [
   {
    path: '/:lang(\\w{2})?/:cat*',
    component: 'route-test-view',
    action: async (_context, _command) => {
      await import('./views/route-test-view');
      return;
    },
}
];
...

• Link to Hilla Route documentation
• Link to Path-To-Regexp