Hm, never seen this problem with 2.3 and a norman LAMP stack (switching to german in backend).
Can you check that the file cms/lang/en_US.php exists? We don't officially support IIS6, do you have access to an IIS7 instance to replicate this issue?
Do you have any additional modules installed, or defined your own lang files in /mysite folder? Did you try ?flush=1?
Sorry for the obvious questions, but I'm running out of ideas, and can't replicate as we don't have an IIS6 instance set up with SS here...
mmhh, I have installed the ecommerce and the picture gallery module.
And there is no lang file in the mysite folder.
But I'm wondering.
Why does SS say, it doesn't know the array $lang(en_US) if the english language is displayed correct ?
Can you tell me in which part of the source the language file is loaded, perhaps I can find out what is going on.
I remember that with 2.2.3 I couldn't change the language to german as well.
But it didn't cause an error, the english language was shown.
One reason for changing to 2.3 was my hope that this will work then :-(
The first line of the source says i8n::....something and somewhere else it is said the internationalisation doesn't work with 2.3
But I've learned somewhere else that the backend language is working anyway.
Perhaps you can give me some areas where I should look and perhaps make a var_dump or so.
It would be a pitty if it doesn't work on IIS6 only because of this single problem.