Why can't I use Korean language on the Muse?

Hi

Adobe Muse CC includes support for self-hosted web fonts. To use a specific font in your Muse site, you will need to install the system font (properly licensed for desktop use) and provide the corresponding web font files (properly licensed for use on a website).

For more details refer to : http://helpx.adobe.com/muse/using/typography.html#Working with Self-hosted web fonts

Give it a try and let us know if you need help or run into issues.