This is a April Fool news
We are very pleased to announce our decision on Yii2 development. Starting April 1st, 2013, the existing Yii2 code will be rewritten using Ruby programming language. Current PHP code will be left as is. After months of consideration, we have decided that Ruby compliments Yii2 better than PHP does.
We will do our best to make transition as easy as possible; you do not need to worry about potential migration problems.
Cheers! The Yii Developer Team