This bug is reported by me, and I know that it's because of '[' and ']'.

..

D:\CI>fossil open tools.db

D:\CI>fossil add tools\中文.txt
ADDED  tools/中文.txt

D:\CI>cd tools

中文.txt 中文[1].txt
        1 file(s) copied.

..

D:\CI>fossil add "tools\中文[1].txt"
fossil: filename contains illegal characters: tools/中文[1].txt

D:\CI>