Changing my locale

[S Salamander]

I'm using GDM to log into KDE.  I've set the locale option on the GDM
login screen to US English (en-us UTF-8) but noticed that in my
Evolution mail reader that the mail folders are being sorted case
sensitively.  This shouldn't be the case if the locale is set as I
thought it  was.  Running 'locale' from my bash prompt shows en_US
UTF-8 for all options, but most are quoted ("en_US UTF-8") leading me
to believe they're not correct and falling back to C.

How do I change the locale 'the right way"?

I'm not at that machine right now, so if the output above is off a
letter or two, I apologize.

Thanks.