What's the difference between addon-lang.iso and livecd.iso?

English Install/Boot/Login
1

openSUSE-11.3-Addon-Lang-i586.iso and openSUSE-11.3-GNOME-LiveCD-i686.iso

Index of /distribution/11.3/iso

And what is openSUSE-11.3-Addon-NonOss-BiArch-i586-x86_64.iso ?

2

Addon-Lang is not an OS install, it contains, as you might guess, language support packages for less commonly installed languages.

Addon-NonOss contains packages for non open source software, in both architectures, since there aren’t many of them and even then it’s less than a full CD.