Win32 UI: Add a runtime created Language submenu.

Inspired by https://github.com/hrydgard/ppsspp/issues/3601.

This also fixes a couple other small bugs such as: the UI wouldn't switch languages in the pause screen. It's created on the fly, so if more languages are added to PPSSPP in the future, it shouldn't require any changes for it to detect new ones.

![Screenshot 01](https://i.minus.com/iTEhrKqRg2oUl.png)