Hey there! At present, if what is being sent to the text box isn't defined in the dictionary, then it won't play a voice file. The language setting isn't factored in at all, only what is being sent to display. In your case, it's a bit of a double edged sword, as you could use that to implement dubbed lines if you also had different voice actors for different languages, but as you correctly guessed, you would need to define keys for each language.
That said, it's a feature I could add to the list once the next goal is hit.