A quicky and nothing code related this time. After upgrading from Windows Phone 8.1 through a number of intermediary Insider builds I found I got more and more problems, even after the 10512 build, and decided to backup, hard reset and then restore my phone. Several sources on the internet says that is a way to solve stability issues. After all, this is still beta stuff. So I followed the procedure, and I ran into a snag - my phone is originally British, it had British keyboards and speech installed, but I wanted USA speech (to get Cortana) and keyboard, as well as a Dutch keyboard, for auto correct and spelling hints.
Whatever I tried, it could not get the phone to download speech or keyboards. It said simply 'error downloading' for speech, and 'text suggestions update for this keyboard didn't download successfully' for the keyboard. Now what? So I backed up the phone again, resetted again, so I would restore it from the exact same version. To no avail.
The key thing to understand is that keyboards and speech are updates to the OS and as such part of the Insiders' preview. And apparently the phone is unregistered from the Insiders rings when you hard reset it. The solution is very simple - hit the Windows Insiders app as soon as it's downloaded (restore will take care of that), and activate the fast ring again. Boom. You can download speech and keyboards.
If I only realized this before I resetted the 2nd time around - that would have saved me half a day.