VueJS addRoutes add more children routes - vue.js

Question

Implementing language switcher and have this last (hope so) missing puzzle.
I have these routes defined:
routes: [
{
path: '/',
redirect: `/en`,
},
{
path: '/:lang',
component: {
render: h => h('router-view')
},
children: [
{
path: '',
name: 'home',
component: Home,
},
],
},
],
And I have some routes coming from backend, I adding these routes to existing like this:
fetchRoutes({commit}) {
axios.get( `${process.env.VUE_APP_API_DOMAIN}/wp-json/api/v1/routes/`).then( r => r.data ).then(routes => {
routes.forEach( (route) => {
router.addRoutes([
{
path: `${route.path}`,
name: `${route.path}`,
component: () => import(/* webpackChunkName: 'pages' */ `./views/${route.component}.vue`),
props: route.props,
},
]);
} );
});
},
This is fine for non-children routes. But I need to put these routes under path: '/:lang', as children.