Hi marcellius.ac,
" Microsoft provides this language in Office, but not in Windows 8(.1) via Control Panel in language input method."
Do you mean there is nowhere to install the language or this specific language is not listed ?
Please refer to the following link to install the language package and configure it .
Change your language or keyboard
http://windows.microsoft.com/en-hk/windows-8/using-multiple-languages
Here is a link for reference of all the language options :
Language packs
http://windows.microsoft.com/en-HK/windows/language-packs#lptabs=win8
If it is not listed ,I am afraid this specific language is not supported.
Best regards