We are working on it and the next version should contain a translation for zh-CN. See https://github.com/rugk/offline-qr-code/pull/175.

BTW, actually, you can always help contributing (or reviewing) your own translation, as we are an open-source project. Just as @Cye3s did there.
For example, we still need a Chinese translation for the add-on listing on addons.mozilla.org here.