It looks like currently .lua files in the plugins folder are loaded using the system text encoding, which defaults to Windows-1252 for English and Portuguese. It should really be using UTF-8 instead. I’ve filed this as a bug, we’ll look into it.
The fix is live as of today, plugin .lua files should now be loaded in as utf-8. Let me know if there are any other situations where utf-8 text gets mangled like this.