Daniel P is right, the messages are not fitting into the fixed-space boxes in the resources DLL.
The quick fix is to change your "system" font so that they do, if possible.
The better change (since you seem to speak Chinese or similar) is to make an improved resource DLL.
There is a lot of detail here:
http://www.gammon.com.au/forum/bbshowpost.php?id=7953
The important point is that the resources are all in the file en.dll (shipped with MUSHclient) and that this file changes contents
extremely rarely (by design).
To support another language you can make a copy of it (eg. as cn.dll for Chinese) and then edit that. Once edited change the "Locale Code" in the File -> Global Preferences -> General to be "CN". Then restart MUSHclient.
Since this file will not be in the download it will persist over new versions of MUSHclient.
To edit the file either get some "binary" resource editor and directly edit cn.dll or get the source of the resource file and edit that and recompile it.
To recompile you can probably use the resource editor which ships as part of Microsoft's Visual Studio "Lite" which is free (although I haven't tried that). Otherwise grab a copy of Visual Studio 6 from somewhere (which is what I use).
The source of the current resource file is here:
https://github.com/nickgammon/mushclient_resources
The main advantage of doing this is you can change all the wording to be in Chinese rather than English (eg. configuration screen, dialogs, menus).
If you are keen you can also edit en.lua (and make it into cn.lua) which is all the internal error and information messages and change those as well, as described in the web post above.