If you switch keyboard layouts, and that changes the key being used, then the ISBoxer Addon will need to be updated so WoW knows what key it is expecting, which requires you to Export to InnerSpace, and this in turn in game will require a /reload to reload the Addon (unless you log out/back in again).
The VKey code 0xDD, which is used to ]} happens to be variable based on Keyboard Layouts.
Used for miscellaneous characters; it can vary by keyboard.
For the US standard keyboard, the ']}' key
ISBoxer itself, stores the VKey code, because, the output of a keyboard driver is the VKey code, and this is what needs to be presented to the receiving process. So ISBoxer's keyboard driver does what it should, and based upon your config, presents the VKey code. Just like the operating system would. The Keyboard Layout sits on top of this, and remaps the VKey code to a display key.
WoW 's keybind config for Addons happens to store the display value of keys, which in this case starts out as ]. So Wow is trying to match ], presumably by doing a reverse lookup of the registered display value to VKey code which is dependent on the current Keyboard Layout in use.
So, WoW is looking for ]. ISBoxer is presenting the VKey code. And the current Key Board layout in question ends up presenting ъ, and the ] and ъ are two different VKey codes. So no match.
Ideally, your ISBoxer config should be configured under the same keyboard layout as you will be playing under. So it all matches.