Of course, after googling a bit more I come across an article on runtime localization.
And followed these steps:
Add the following to the compiler arguments to specify the supported locales and their path:
(In Flex Builder, select project and go properties -> Flex Compiler -> Additional Compiler Arguments)
-locale=en_CA,fr_CA -source-path=locale/{locale}
Create the following files:
src/locale/en_CA/resources.properties
src/locale/fr_CA/resources.properties
And then the compiler complains: unable to open 'C:\Program Files\Adobe\Flex Builder 3\sdks\3.1.0\frameworks\locale\en_CA'
Which looks to be related to bug SDK-12507
Work around:
In the sdks\3.1.0\bin
directory, execute the following commands:
copylocale en_US en_CA
copylocale en_US fr_CA
This will create the locale directories in the Flex Builder installation and build some required resources into them.
Then in your .mxml
files, reference the resource bundle:
<mx:Metadata>
[ResourceBundle("resources")]
</mx:Metadata>
And internationalize the strings:
<mx:TitleWindow title="Window Title">
becomes:
<mx:TitleWindow
title="{resourceManager.getString('resources', 'windowTitle')}">
and
var name:String = "Name";
becomes:
var name:String = resourceManager.getString("resources", "name");
And in your src/locale/en_CA/resources.properties
file:
windowTitle=Window Title
name=Name