you can't go from 8.6 to 9x in any language.
you say you have 'OS 9.1 for International English' which suggests it is on disk. if so, do a clean install and maybe while you're at it you might as well initialize your HD.
make sure you back up your personal files first.
insert 9.1 disk, go to the start-up folder, click 9.1 disk and restart. this means you'll be booting from the 9.1 disk so you can then wipe the HD and clean install 9.1
make sure it's compatable with your computer though. the 9.1 disks i got were for a non-DVD iMac, so i had to work around that problem.
best to do research on this before jumping in. and/or make sure you have your original 8.6 disks just in case.