If you create Mediawiki:strJSmsg.js and copy the code into that then add an import statement to Common.js it seems to do something but now I get:
"Webpage error details
User Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; WOW64; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.648; .NET CLR 3.5.21022; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729; .NET4.0C; .NET4.0E)
Timestamp: Mon, 12 Sep 2011 10:24:21 UTC
Message: Object expected
Line: 1180
Char: 1
Code: 0
URI: http://<servername>/ict-test-wiki/skins/common/wikibits.js?270
Message: 'this.lang.button label' is null or not an object
Line: 182
Char: 2
Code: 0
URI: http://<servername>/ict-test-wiki/extensions/JobSchEd/edit_calend.modules.mini.js?1
Message: 'this.lang.gantt not found' is null or not an object
Line: 192
Char: 3
Code: 0
URI: http://<servername>/ict-test-wiki/extensions/JobSchEd/edit_calend.modules.mini.js?1