Look in the Project Property page, Application tab. You should see a 'Locale' listbox - just check en_US and es_ES for English and Spanish.
Then click on the Libraries tab, then Resource Bundles. Right click and the Add. Then click on the added line to edit it to the name of the bundle.
You will probably need to set a library path so that the compiler can find it - click on Paths then Library Paths and do the same.
The Paths listbox editing isn't that great and I think we might try and improve that for the next version of Amethyst.
If something goes wrong (typically a path or something) it can be a bit tricky to find out what's happened - the Adobe compiler doesn't produce the clearest error messages in the world - so the thing to do here is to pick out the command line that's output in the Output window:
"C:\Flex SDKs\flex_sdk_18.104.22.16801B\bin\mxmlc.exe" -incremental=true -load-config+="C:\Users\dermot\AppData\Local\Temp\FlexApplication.xml" -output "C:\Data\Amethyst_2_Test\FlexApplication\FlexApplication\bin\Debug\FlexApplication.swf" -- "C:\Data\Amethyst_2_Test\FlexApplication\FlexApplication\bin\Debug\temp\src\FlexApplication.mxml"
and look at the xml configuration file "C:\Users\dermot\AppData\Local\Temp\FlexApplication.xml". This is what the compiler uses and you can edit this directly and use the command line in a command prompt box (aka DOS box) to repeatedly re-run the compilation until you get it right. Then put the settings back into Amethyst.
I've done this using Spanish and English some time ago, so I know it works. You don't need ant.