Windows 8 Speech Recognition Language

This probably has not changed from Windows 7, where the speech recognition language is tied to the language specified for the OS. Try getting and installing the English-US language pack and it should become available as an option for speech rec. Here is a blog that discusses installing language packs in Windows 8.

Finally found the solution:

1) Download the x64 Language Pack DVD ISO

2) Navigate to the EN-US folder and copy the lp.cab file to a local hard drive

3) Rename the .cab file to .mlc and double click it

4) Run through the wizard to install the language

5) Open Advanced Speech Options and EN-US is now available