That is odd that the error is related to using t.forEach as I don't see that in your code snippet.
Maybe it is calling that method elsewhere or when i18n.init() runs, or inside the i18n.changeLanguage(selectedLanguage) 
For your use case. I would create a Variable, this will be the object that you are passing into i18n when you run the .init() method from above.
Then in your text component, you would key into this object with the language key from the dropdown.
