How could I translate a module?

Hello, guys. The thing is this, I want my application to be i18n, and I set its source language “zh_cn”, while its target language “zh_cn” too. And then the yii framework works well, it translates all the information to be chinese, but when I envoled a extension called “yii-user”, problem happened. The translation didn’t take effect at all! Because the source language and the target language is the same! But, actually, the application is written in Chinese, but the extension is not. I think yii framework itself works well, because it actually translates although the source language is the same as the target language, there must be some information stored to mark that the yii framework itself is written in en_us.But what about the extension? May you can help me, and forgive me for my poor English, Thank you all. :D

Forgive me if it is a stupid question, but did you check if the extension uses "Yii::t()" to print system strings?