[Vuejs]-Where to execute method to persist locale change in nuxt-i18n?

Try call it in plugin

export default async function ({app, store}) {
  // on change locale
  app.i18n.beforeLanguageSwitch = (oldLocale, newLocale) => {
    ...
  }
}

nuxt.config.js

  plugins: [
    '~/plugins/i18n.js'
  ],