Microsoft and 343 Industries released the DEMO version of the Halo Wars 2 what you can download to your Xbox One from today in all regions IF you are Xbox Live Gold member. According to the press-release the Windows 10 version demo comes in a later date.
In the DEMO you can try an early campaign and it supports the Japanese subtitle next to the English. If you want to try if before you buy it, now you can do it.
You can find the DEMO in here: https://www.microsoft.com/en-US/store/p/halo-wars-2/BNQ1T5HWZWWC