Get the Win8.1 Update CoreSingleLang en-US ISO's (Please refer to post below for download)
Get the win8.1 language pack cab's , get the individual cab for your language instead of the full ISO, make sure it's the correct architecture (X64/X86)
Get the win8.1 update lanaguage pack update:
Install the CoreSL, generic key: Y9NXP-XT8MV-PT9TG-97CT3-9D6TC
After installation, in my case the LP cab is in users\bill\download ; and I convert to zh-CN (change to your lang code)
Then add the "Win8.1 Language Pack Update" with same procedure.
Reboot after LP cab installation, CMD(Admin), enter : bcdedit /set {current} locale zh-CNbcdboot %WinDir% /l zh-CN
Open regedit, goto : HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Contro l\MUI\UILanguages
and remove all items in the en-US key
In Control Panel, set your location and time-zone, and change System Locale to your locale
Reboot, and it's done, since it's a win8.1 LP cab, some items would still be displayed in English.
(Update: if you have also added "Win8.1 Language Pack Update", then translation would be complete).
4. Windows 8.1 with Update x86 (Single Language/CoreSingleLanguage)
6.3.9600.17050.winblue_refresh.140317-1640_x86fre_client-coresinglelanguage_zh-cn.iso
Size: 3128371200 bytes
MD5: EFADA7B7FB775E193819CA6E243B72BA
SHA1: 934F3613C43D5DFD29F6167BE1121A40388DE4FF
CRC32: 12099E60
generic key: Y9NXP-XT8MV-PT9TG-97CT3-9D6TC http://pan.baidu.com/s/1i3JsLbn
5. Windows 8.1 with Update x64 (Single Language/CoreSingleLanguage)
6.3.9600.17050.winblue_refresh.140317-1640_amd64fre_client-coresinglelanguage_en-us.iso
generic key: Y9NXP-XT8MV-PT9TG-97CT3-9D6TC
..... not uploaded yet ......
Windows 8.1 with Update x86 (Single Language/CoreSingleLanguage)
6.3.9600.17050.winblue_refresh.140317-1640_x86fre_client-coresinglelanguage_en-us.iso
generic key: Y9NXP-XT8MV-PT9TG-97CT3-9D6TC http://pan.baidu.com/s/1kT5H38N