I genuinely don't understand this comment or the reason for writing it as a hook or a separate component in the article

Why wouldn't you just write it as a function with data and context being passed through as arguments? Isn't it much simpler to write a pure function and test that function than render a component and test it? If you simply write a function that accepts the locale, the string and context, does the translator magic and returns the translated text, would you not then just need to write a unit test simply to make sure you're getting the expected output? Why the abstraction into hooks and then further into a separate component that you then have to render?