We now know that MemPad both supports Unicode, and has Drag&Drop
MemPad does not support UNICODE, I am sorry to say (I am the author).
UNICODE uses a multi byte code that covers all languages of the planet, and even allows displaying Chinese, Russian and English on the same page. For a programmer this is more difficult to handle than ANSI, which stores all characters in a single byte.
ANSI includes the standard English character set (first half of the 256 codes) as well as a set of special characters that can be configured through Windows' regional settings. The "Western" set includes all sorts of western european special characters (see Charmap.exe).
Windows programs usually handle all these characters, including conversions upper/lower case. For regions like Russia or Greece the "Western" set is replaced with a regional set, which works nicely, and still supports ANSI English, but you cannot mix Russian and German umlauts, for example.
Programs without UNICODE support can even handle Chinese or Japanese, because those Windows versions have emulations that support 2-byte codes and pretend it's normal single byte code. However that is likely to fail on memory string operations.
BTW: Another issue is the OEM character set ("DOS") that is used for Windows console programs ..