Now that BabelMap has made its way to official apps, it would be great if BabelPad could follow. Created by the same author it is, in my opinion, the best plain text editor for "Unicode-intensive" purposes.
License: Free for personal or commercial use
Description (from the website): BabelPad is a free Unicode text editor for Windows that supports the proper rendering of most complex scripts, and allows you to assign different fonts to different scripts in order to facilitate multi-script text editing. It also provides many useful features and special utilities.