Using old interop I can access shape.TextFrame.TextRange.LanguageID. I see the preview of office.js for PowerPoint expose TextRange with a limited set of properties. Any plans to expose LanguageID or...
I'm looking also for other text properties like paragraph line spacing and some of the formatting like superscript, subscript, strikethrough. Ultimately all of the formatting that can be done in the UI should be exposed also in the API otherwise we will always come short.