How to react to @nuxt-i18n locale changes inside the setup function

If you are using Nuxt v2, nuxt-i18n and you want to react to i18n object changes inside the setup function, let's say, a language change, this blog will teach you how.

I also cover how to use localized messages inside the setup function in this other article.

Let's say for instance, you want to craft a special url to point to other site, but you want to keep the current language of your user in the link:

setup(props, ctx) {

// all the stuff is in the root
const { root } = ctx;

const mapedURL = ref("");
const baseUrl = "https://my.other-site.com";

function setUrl() {
    const isInSpanish = ctx.root.$i18n.localeProperties.code == "es";
    if (isInSpanish) {
        mapedURL.value = baseUrl;
    } else {
        mapedURL.value = baseUrl + "/en/";
    }
}



function triggerWatch() {
    // keep traking on language changes when page loads
    // hint: this dosen't work in edge properties like *.localeProperties.code
    watch(ctx.root.$i18n.localeProperties, (newV, oldV) => {
        setUrl();
    });
}

// init when page loads
onMounted(() => {

    // this watch will brake in the server so ignore there
    if (!process.client) {
        return;
    }

    setUrl();
    triggerWatch();
});

  return {
    mapedURL
  }
}

Tested in Nuxt v2 and nuxt-i18n v7. That's it folks.