Add multilingual prompt support

[phly95]

When learning a language, prompts may be multilingual. Currently, there's no way to specify that a prompt is of two or more languages.

An example of a multilingual prompt may be "Write a Japanese sentence using the words 青い, 空, and 天気."

This could also be used for translations, since LLMs can be good at translation without needing external translation tools. In fact, I'd say GPT-3 is better than Google Translate and DeepL most of the time.