I got 0x80070020 error message every time when I tried to install a second keyboard on my lumia 640 LTE running 10.10586.107. Doesn't windows 10 support Chinese input?
I reverted it back to W8.1 using WDRT, installed the keyboard I wanted, and upgraded OS to 10.0.10586.107. Everything works now.
Posted from Windows 8.1