Hey suweihua,

I tried to reproduce it but login worked for me. I changed the language on my Piwik instance to "chinese simplified". Then I opened Piwik Mobile (language English), added an account, got the list of available websites and viewed some reports. App was also working when changing the language in Piwik Mobile to "chinese simplified".

Have you any special characters in your username or password? Did you get any error?

The graphs indeed can't print chinese simplified. I think I have to create a separate ticket for this issue.

Chinese fonts in graphs not working is covered in: #2704

(In [5938]) refs #2723 load a default locale if we do not have a translation for the locale of the device

There was an issue with older Piwik Server versions (for example Piwik 1.0). An error occured if the current language was not available on the Piwik Server Version. I think the language is available in your case since it works with chinese simplified. Example: You choose "chinese simplified" in Piwik Mobile App (or your device has the locale "chinese simplified") but the locale/language is not available on the Piwik Server. The Piwik API returned an error (HTML Page with Error Description -> Results in parse error). In such a case one should just update Piwik to the latest version.

Another issue which possibly relates to this issue is #2735 ?

Please reopen this ticket if you are still able to reproduce the error after upgrading to Piwik 1.7 and Piwik Mobile 1.7 (which will be available soon)