External Speech Recognition APIs

I am pretty new to Unity, but I am part of a project where it's my responsibility to look into utilizing voice recognition to all the user to dictate in various languages and take that text to compare with an expected answer.

I found out that Unity has a built-in API it seems in unityengine.windows.speech, but I don't know to what extent this is effective or what the actual API is. Also, I know it's apparently a relatively new feature in Unity, but I have tried Google (yes, I have googled this) so many times with getting oddly very few if any results that clearly explain how to do much with voice recognition. I have gotten the keyword recognizer to work at least.

So, my questions are,

1) What API is unityengine.windows.speech, and does it support languages other than English? If so, how do I utilize them?

2) How do I utilize external speech recognition APIs such as Google Cloud Speech Recognition or Cortana? I can use Windows 10, so I heard that Cortana is free to use for development on Windows 10 (not sure if that's correct or not though).

3) Do you have any suggestions on APIs that are either low in cost or effective when accurate dictation is important? Or that are easier to integrate into Unity?

I'm sure I might have more questions in mind, and I'm sorry if I am asking something that is easily answered elsewhere, but I just haven't had much luck in finding them. If someone could point me to the right place, that would be great too. Thank you!

Note: I posted this in the VR forum as well since we are working on a VR project, but I felt this was probably the more correct forum to ask about this since I'd like to know how to do it in general.