From what I gather, any external ActionScript script you may have that you are linking to through an #include statement, you may need to use this code to allow certain characters to be read in the document as UTF-8.  I ran into this issue about a month ago, and a co-worker of mine knew the solution.  It's something I find is rarely used and easily forgotten:

//!-- UTF8

Taken from

To create a document that contains multiple languages, use the #include action.

Use an application that supports UTF‑8 encoding, such as Dreamweaver, to save the text file in UTF‑8 format.

To identify the file as Unicode to the Flash authoring tool, include the following header as the first line of the file:

//!-- UTF8 Note: Include a space after the second dash (-).

I hope that helps some of you who may have struggled with this ;-).