dreamweaver disable "language for non unicode programs" detection
Solution 1:
As detailed here, you should be able to set the default encoding to UTF-8 (preferably without BOM) in the Preferences. I don't think this is affected by the system codepage.
The system-codepage-sniffing to change UI language is sad. I'm seen this commonly in poorly-written Japanese programs, but for DW to be doing that too is disappointing. Applications that do this need to be taken outside and shot. To get around it, you can use apploc to change the codepage a particular application sees when it runs.