Okay, I think I figured it out. There are two English language files in "C:\Program Files (x86)\Stardock\Start11\lang," and in both files, at the bottom appears the following:
;Added in 2.11
"Task Manager"="Task-Manager"
I hadn't updated since the 2.11 Beta, which is why I didn't see the hyphen. So I installed the 2.11 Release version, and sure enough my taskbar context menu now says "Task-Manager."
I'm not sure who decided this, but it needs to be fixed!
EDIT: I opened both language files and deleted the lines,
;Added in 2.11
"Task Manager"="Task-Manager"
and now Task Manager displays correctly.