How to set MXMLC (FCSH) to English (on Windows)
If you are working in the Netherlands on a pc with MXMLC (FCSH) you probably get all your errors in Dutch, like:
“Functie heeft geen hoofdtekst.” or “Waarde van het type Function is gebruikt waar type void werd verwacht. Mogelijk ontbreken ronde haakjes () na deze functieverwijzing”.
Funny, but not very handy since most help and documentation is in English. So I wanted my errors in English. FCSH does not have any option to change the language. Changing Windows to English doesn’t change anything and setting the location to U.S. doesn’t help either. Finally we found out that setting the format to”English (United States)” will set MXMLC to English:

Unfortunately this will also change your number, currency, time and data formatting. But you can customize this back to the Dutch settings.
March 25th, 2010 at 16:44
Unfortunately this trick doesn’t work for Extension Manager bug. The Extension Manager still installs all extension in to the ‘nl’ folder instead of the ‘en’ folder.
August 10th, 2010 at 23:37
Hahahahha, dit probleem had ik vandaag dus en nu lees ik ‘t toevallig 5 uur later hier ook. Ben nu met een multitouch game bezig in flash, dus moet opeens op windows 7 developen……. argh….. dat is echt rocketscience voor een mac adept.
November 3rd, 2010 at 15:13
Another way to enforce this is to browse to your local FLEX SDK installation, then go to /flex/lib and remove the mxmlc.jar’s with the unwanted locale.
Removing just the mxmlc_nl.jar seems to do the trick, but there’s some other stuff (I see batik and xerces in my Flex 4.0) that you might want to check out: I’m not sure if Flex does a global ‘revert to global locale’ switch, or if it checks on a per-resource basis.
Also note there’s localized stuff in the /flex/framework that might show up and interfere lateron.