The recommended way to add support for a new locale is to:

Create an Ext plugin that adds a language properties file for the desired locale

Create an Ext plugin that adds a language properties file for the desired locale and implements a servlet filter mapping using IlSnFilter

Create a hook plugin that adds a language properties file for the desired locale and implements a servlet filter hook to invoke IlSnFilter through PortalClassLoaderFilter

Create a portlet plugin that overrides the core language filter to recognize the desired locale