To further Mitch’s suggestion, a “What” command on a text curve can report a perfectly “valid (closed) curve” but I’ve come across my share of TrueType curves that exhibited problem spots that would result in bad solid extrusions. They often occur where the curves make a sharp kink. Often so small, it’s only visible with a lot of zooming & inspecting. Here’s an exaggerated example:
As for the sideways Chinese text, I’d certainly classify that as a bug. Possibly the Text Object dialog box is taking hinting code from the font? I’d guess that some of the Asian Unicode characters contain hinting that they’re sometimes laid out vertically and Rhino is improperly using this? When the text is pasted into Notepad.exe from Windows Clipboard, it’s oriented correctly and entered in a valid left-to-right fashion. Heck, even pasting clipboard contents into Rhino’s Notes window behaves properly like Notepad.
Just checked… looks like a bug with Chinese and Japanese characters. Korean pastes in the proper direction.