Localized routes in koa

I'm developing a site with multiple languages. Some routes will therefore also have to be localized and I'm not sure how to do this properly.

I'm using @koa/router for routing.

For this example it's only English and Swedish but the site will handle more languages.

I can setup routes to match words in different languages like

router.get('/(create-account|skapa-konto)/', (ctx, next) => {
  ctx.body = translate('signup_welcome');
  await next();
});

But, I want the English site to only respond to '/sign-up' and send 404 for '/skapa-konto' (and vice versa).

In the real world the route would point to some controller function. So if I set up individual routes for each language I would have to change all localized routes manually should the controller function change in the future. That's something I would like to avoid ;)

Any suggestions?

I ended up solving this by extending the Router like this:

const LocalizedRouter = class extends Router {
    /**
     * Set up route mapping
     * @param {object} options
     */
    constructor(options) {
        if (!Array.isArray(options.languages)) {
            throw new TypeError('Languages must be of type Array');
        }

        super(options);
        this.languages = options.languages;
    }

    /**
     * Router function for GET method
     * @param {string | Object<string, string>} RouteCollection
     */
    get(routes, func) {
        if (typeof(routes) === 'string') {
            super.get(routes, func);
            return;
        }
        if (typeof(routes) === 'object') {
            for(const key in routes) {
                if(!this.languages.includes(key)) {
                    continue;
                }
                if(typeof(func) !== 'function') {
                    throw new TypeError('Middleware must be a function');
                }
                const checkLanguageAndMount = async (ctx, next) => {
                    if(ctx.state.lang !== key) {
                        return next();
                    }
                    return func(ctx, next);
                };

                super.get(routes[key], checkLanguageAndMount);
            }
            return;
        }
        throw new TypeError('"Routes" must be a string or an object');
    }
};

I can then set up my routes like this:

const myRouter = new LocalizedRouter({
    languages: ['en', 'sv']
});

myRouter.get({
    'en': '/create-account',
    'sv': '/skapa-konto'
}, (ctx, next) => {
  ctx.body = translate('signup_welcome');
  await next();
};

This can probably be cleaned up but it does solve what I wanted to do.

EDIT: Fixed bug that caused 404 if two languages had identical paths