I came across a strange issue recently when attempting to install the Remote Server Admin Tools (RSAT) on a fully patched Windows 8 VM (The issue was encountered on VM but I assume I would have the same issue with a physical desktop / laptop). I download the x64 version from Microsoft and proceeded to install. After accepting the license agreement the installation started and then completed straight away:
Browse to English and double click. From there select the English (United States)
You should now see both English (United Kingdom) and English (United States).
Click on the English (United States) and select the option to Download and install language pack (accept any prompts along the way):
Once the language pack has downloaded and installed simply start the RSAT installation again and it should install correctly this time:
Once finished you can install the required RSAT tool via Programs and Features.