偏好语言可以按会话，用户或作为网站默认来进行设定。你也可以使用一个请求参量进行覆盖从而改变语言设定。

The preferred language can be set per session, per user, as a site default and you can change it also with a override with a request parameter.

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应为各参量分派默认值。

A default should be assigned to each parameter.

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如未被定义，特定外观主题的默认外观主题参量将被使用；反之参量应为无尽的。

If not specified, the default theme parameters for the specified theme are used. if specified, the parameters should be exhaustive.

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