Moving from compile time to run time locales

So you just woke up and realized that users are complaining about slow load times and you need to make you SWF file leaner ... where do you start?

Baby Step # 1: If you have localized your application then begin by removing all the properties files for the various locales and only loading what any given user needs at a given time.

The best place to start such an endeavor is at Adobe's live help: Using Flex 4 > Enhancing usability > Localization

The link above is helpful and critical in many ways but it doesn't talk about developers who use Maven and what they need to start doing differently in their build process before they start worrying about how to load the localized SWF files.

If you are using flexmojos then a part of your pom.xml probably looks something like:
        <configuration>
          ...
          <compiledLocales>
              <locale>en_US</locale>
              <locale>de_DE</locale>
          </compiledLocales>
          <mergeResourceBundle>true</mergeResourceBundle>
          <resourceBundlePath>${basedir}/src/main/flex/locale/{locale}</resourceBundlePath>
        </configuration>

Initially this may have seemed great as it did the job fast but now you need to change this to something like:
        <configuration>
          ...
          <runtimeLocales>
              <locale>en_US</locale>
              <locale>de_DE</locale>
          </runtimeLocales>
          <mergeResourceBundle>false</mergeResourceBundle>
          <resourceBundlePath>${basedir}/src/main/flex/locale/{locale}</resourceBundlePath>
        </configuration>
A few helpful flexmojos references can be found here and here.

Also in the project where you put together your war file, you need to get the runtime locales' SWF files over in addition to the application. So follow the instructions here, with a few more details listed here.

Now if you head over to the adobe site I mentioned earlier and follow their instructions, you may end up with:

Error: Unable to load resource module from ...

This happened when using:

var resourceModuleURL:String = "locales/myApp-version-locale.swf";
var resourceManager:IResourceManager = ResourceManager.getInstance();
var eventDispatcher:IEventDispatcher = resourceManager.loadResourceModule(resourceModuleURL);

Even though it may seem logical to try and reference the resource SWF as if it was a relative file and hope that Flex will fill in the blanks, that is not the case ... so a quick & dirty solution can be to use localhost like so:

var resourceModuleURL:String = "http://localhost:8080/myApp/locales/myApp-version-locale.swf";
var resourceManager:IResourceManager = ResourceManager.getInstance();
var eventDispatcher:IEventDispatcher = resourceManager.loadResourceModule(resourceModuleURL);

And you'll have a working solution ... mind you that I've left out some critical code that Adobe cover in their article which come after the few lines I've outlined here.

If it is unappealing to use localhost, you can look into configuring crossdomail.xml or refer to these great articles for an alternative approach:
1) Flex: Loading Remote Modules Throws the following: Error: Unable to load resource module from…
2) Loading a Remote Module into a Local App