Text CAPTCHA has been an effective means to protect online systems from spams and abuses caused by automatic scripts which pretend to be human beings. However, nearly all the Text CAPTCHA designs in nowadays are based on English characters, which may not be the most user-friendly option for non-English speakers. Therefore, under the background of globalization, there is an increasing interest in designing local-language CAPTCHA, which is expected to be more usable for native speakers. However, systematic studies on the usability of localized CAPTCHAs are rare, and a general procedure for the design of usable localized CAPTCHA is still unavailable. Here, we comprehensively explored the design of CAPTCHAs based on Chinese characters from a usability perspective: cognitive processes of solving alphanumeric and Chinese CAPTCHAs are analyzed, followed by a usability comparison of those two types of CAPTCHAs and the evaluation of intrinsic design factors of Chinese CAPTCHAs. It was found that Chinese CAPTCHAs could be equally usable comparing with alphanumeric ones. Meanwhile, guidelines for the design of usable Chinese CAPTCHAs were also presented. Moreover, those design practices were also summarized as a general procedure which is expected to be applicable for the design of CAPTCHAs based on other languages.