In case of a multilingual application, one might consider it a reasonable approach to store the preferred language of the user in a session variable, and after that, every time a page is requested, to check this session variable and render the page in the indicated language.
This tutorial shows a Yii-way of doing this.
We implement an event handler for the onBeginRequest event; as the name of the event suggests, this event handler will be called at the beginning of each request, so its a good place to check whether a language is provided (via post, session or cookie) and set the application language accordingly.
We also implement a simple Language-Selector Widget, which can render the language options as ajax-links or as a drop-down list.
A lot of people have written posts on integrating Yii and WordPress. This article combines goncin's approach with an article I read about integrating Symfony and WordPress and applies it all to Yii and WordPress.
A dropdown list can be used to select a value, based on which we can filter the data to be displayed. For example, the extension page has a dropdown list to filter the displayed extensions according to the selected category.