Using pop-up window and I18N, error in render: “typeerror: cannot read property” appears_ T ‘of undefined’ solution

First, make sure to hang Vue under window.vm in main.js (the name of VM can be customized)

window.vm = new Vue({
  el: '#app',
  i18n,
  router,
  store,
  render: h => h(App)
})

Secondly, when writing multi language in the pop-up box, you need to add VM.
for example, when writing multi language, you need to write {$t ('xxxxx ')} or this. $t ('xxx')
then you need to write {VM. $t ('xxxxx ')} or this. VM. $t ('xxxxx') or this