could someone test support for Asian languages in nanogui port?

[drug]

I port nanogui, but besides porting I'd like to improve it using great 
capabilities of D language provides. One of them is utf support, so I 
added support for Asian languages to nanogui.TextBox. But I'm not sure 
I've did it well and so I'd like to ask someone to test it using the 
following:
```
git clone --recursive https://github.com/drug007/nanogui.git
cd nanogui
git checkout textbox # TextBox exists in this branch only
dub --config=sdl # Keyboard events provided only by SDL2 backend only
```

On the right side there will be a window with four text boxes with 
russian, english, japanese and chinese text respectively. It would be 
nice to get some feedback from users - probably I did something totally 
wrong. Also I'm curious does it worth efforts?