Known Issues - Windows 10 Mobile Insider Preview Build 14959
If you used the previous ‘date change’ workaround to update to Build 14951 or Build 14955: Please don’t use it any longer! The Microsoft account (MSA) ticket on your device needs to expire and then you’ll be offered today’s build. If you changed your date by 30 years… you’ll want to do a device reset.
You will be unable to install additional languages, keyboards, and speech packs on your phone for the next few weeks. If you have existing languages, keyboards, and speech packs installed – they will carry over when you update to new builds. You just can’t install any new ones. If you do a hard reset of your phone on these builds – you will also be unable to install additional languages, keyboards, and speech packs. You can use Windows Device Recovery Tool to go back to Windows Phone 8.1 or Windows 10 Mobile, install any languages, keyboards, and speech packs you need and then update to the latest build in the Fast ring as a workaround.