So to follow-up, I got support to enable Endpoints in Studio. I created a basic endpoint using the sample you gave me almost exactly as-is, then tested it and it works great. Then I created the ajax call in my javascript to use the endpoint to fetch a text key, and this is working.
Your original reply said it would return the text value in the language of the user accessing the endpoint, which I have confirmed. However, in our single-instance language community structure, all our users have their language set to English, and instead we have created categories pages for each language community and assigned the language pack to that category page, which Lithium then properly recognizes down the hierarchy for the most part.
However, because of this way we are setup I want the endpoint to recognize the language of the PAGE it is being called from, NOT the user that is calling it, in order to get my properly translated text.
Is this possible?