Plugin Localization doesn't work for me?

I use POEdit to make localize file: subscribe-by-email-zh_TW.po & subscribe-by-email-zh_TW.mo , and my wordpress is set in zh_TW Chinese mode; however, the Subscribe by Email plugin msg didn't show correct localized text.

Is that my filename - subscribe-by-email-zh_TW.po get wrong?

Thanks!

dAb