The Bat! e-mail client [url removed, login to view] supports macros in message templates. While most of the macros are handled internally by The Bat!, there is an opportunity to create plugins to implement custom macros. The API to create plugins is available at [url removed, login to view]
We need a Delphi source code for a plugin to implement the %SWITCH_KEYBOARD_LAYOUT macro to switch keyboard input language in the message editor, e.g. %SWITCH_KEYBOARD_LAYOUT="RU" will switch the language to Russian.
The plugin source code should be neat, should not use any third-party library.