@kzssc: This occurred in the latest Zotero beta version when using a non-US-English locale. It's fixed in the latest beta, so you can just update to that, but if you don't mean to be running a beta, you should switch back to the latest release version from the download page. If you do mean to be using a beta, be sure to always say so (as you usually have before) when reporting problems here.

(Betas usually work fine in non-US-English locales, but every once in a while a version might get pushed before US English string changes have been merged, and then this happens.)