Yes and no.
The only way to convert several files at once is to use the command line option. There is no way to do it using the Calibre GUI.
You need to open a terminal (e.g. PowerShell on Windows, xterm on Unix) on your computer and change directory to the root of all your epub files.
To convert from simplified to traditional vertical text, enter the command at the shell prompt:
Code:
calibre-debug --run-plugin "Chinese Text Conversion" -- -ol tw -il cn -d s2t -qt e -td v -tdo r -a T **/*.epub
This will convert all epub files in that directory and below. The new files will have the same name as the old files except add a "T" to the end of the name. replace "epub" with "azw3" in the command if you have Kindle files. See post #28 above.