The plugin is available in the download section.

Main features:

(rus)
cp1251,cp866,koi8ru,iso,mac character encoding conversions

(international)
win<->dos(oem) character encoding conversions

(global features)

1/ user symbol table support

There are such strings in 'ConvertExt.ini' file:

[Symbols]
;default symbols (english)
SymbL0=`1234567890-=\qwertyuiop[]asdfghjkl;'zxcvbnm,./
SymbH0=~!@#$%^&*()_+|QWERTYUIOP{}ASDFGHJKL:"ZXCVBNM<>?
;alternative symbols 1 (F9)
SymbL1=ё1234567890-=\йцукенгшщзхъфывапролджэячсмитьбю.
SymbH1=Ё!"№;%:?*()_+/ЙЦУКЕНГШЩЗХЪФЫВАПРОЛДЖЭЯЧСМИТЬБЮ,

If 'ENG <-> ALT.1' option is active (F9 in notepad++ was pressed), then any pressed character  which could be found in SymbL0 or SymbH0 (in .ini-file) will be replaced by a character on the same position in SymbL1 or SymbH1. If a pressed character is not found in SymbL0 or SymbH0, but could be found in SymbL1 or SymbH1, it will be replaced by a corresponding character in SymbL0 or SymbH0.
I use this feature as a switch between english and russian (F9) and between english and ukrainian (Alt+F9). I don't like to use system language switch (Alt+Shift or Ctrl+Shift), because I have to use these key combination twice every time (english->russian->ukraininan->english).
With F9 and Alt+F9 internal swithes I can use russian or ukrainian characters even when there is no such language installed in Windows.

2/ smart autobrackets

Currently it means (), [], {} and "" before the following charactes:
0x0D, 0x0A, 0x00, ' ', '\t', '.', ',', '!', '?', '/', ':', ';', '<', '>' or another bracket
("" after 0x0D, 0x0A, 0x00, ' ', '\t' only).

3/ opening current file in external hex-editor

The following string in the .ini file:

HexEditor=xvi32\xvi32.exe

specifies a relative path of external hex-editor (relative to notepad++.exe)

You can also specify an absolute path, for example:

HexEditor=C:\Program Files\WinHex\WinHex.exe

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Responses and suggestions are welcome :)