I’m not able to access your page —?it’s giving a 403 Forbidden error.
Anyway, I think I know the issue. “Busy” is not in the plugin at all. I’m guessing it’s content of your feed itself.
The plugin does not (and cannot) translate the text of your feed data; it relies on built-in translations in WordPress for day and month names, and the rest of the text strings contained within the code of the plugin itself are in our translation files. But any text that comes from your source feed gets displayed as-is.
If your calendar is only indicating whether times are blocked out as busy (that is, not displaying specific event details), then you can use the maskinfo parameter to change what gets displayed:
https://icscalendar.com/icsdocs/#maskinfo
If you’d like to have more conditional control over what gets displayed, there are two options. The free ICS Calendar plugin has some hooks that allow you to manipulate the output (PHP coding required):
https://icscalendar.com/developer/
The Pro version also has a Regular Expressions tool that allows you to do some conditional text replacement using regex format within the Calendar Builder tool, rather than having to edit any theme/plugin PHP code:
https://icscalendar.com/icsdocs/#regex
