Y3 is a language test version.
It's being tested by the Chinese, Japanese and Korean translators. The language support will be released in a public test patch very soon but it made sense to do a limited test first, as there were plenty of issues to sort out, and I didn't need to hear the same bug reports from too many people. These are not easy languages to support!
The characters must be selected from a font installed on the computer, then they must be drawn onto a bitmap when required and stored on one of a few special character textures in memory. When they are no longer in use, them must be removed from the texture to make way for new characters. The frame rate is just as high as with Latin Characters only. I think the frame rate is very slightly improved with Latin / Cyrillic / Greek characters as well.
This is because Chinese has something like 20,000 characters, not just 26.
They cannot all be in memory at the same time.