Labels can use any language that supports the current font.
In your case, the problem is that the request to Google Places / Nearby Search is using English.
Unfortunately, in the current version of Online Maps there is no way to change the language of request to Google Places / Nearby Search.
We have just added this parameter and in the next version you will be able to specify the language of request.
If you want to get it quickly and not wait for the release of a new version of the asset, email me (support@infinity-code.com), and I will send you a modified script.

I was able to switch languages on the map. However, the label language of the marker seems to be English only.

Is it possible to set the "result.name" of the marker created by "OnlineMapsMarkerManager.CreateItem" to something other than English?

I would like to switch the label on the apple marker to Japanese.