On Windows 10, if you are using Japanese 2-byte characters or Korean characters in Theme name, the language characters are rendered as empty squares.
If, however, you are using the language characters same as the language version of Windows 10, you do not encounter this issue.
On Korean version of Windows 10: Korean language characters render correctly but Japanese 2-byte characters render as tofu/empty squares
To resolve the issue, add the relevant language pack for your OS. For more information refer KB article: https://helpx.adobe.com/creative-cloud/kb/Korean-and-Japanese-characters-rendered-as-tofu- in-Packager-UI.html