Your comments

Sorry, but I don't plan to add more localizations at the moment.
Are you sure you are in the right support forum? This one is for the app "Textastic" which is only available for iOS and Mac. 
This should already be the case.

I slightly changed the undo behavior in Textastic 3.0 which is currently waiting for review at Apple and should be available on the Mac App Store in a few days. Please let me know if the new version still has this problem once it is released.
I added it to version 3.0 of Textastic for Mac (currently waiting for review at Apple) and plan to add it to the iOS version. 
Thanks for the example file. The encoding routine didn't properly handle the standalone attribute that follows the encoding attribute in the XML header. 

This bug will be fixed in the next update.
Hello,

if you have a website open in Safari, you can replace the "http://" part with "textastic://" and hit return. This will download the website in Textastic.

This is documented in more detail at the bottom of this page: http://www.textasticapp.com/v4/manual/x-callback-u...
Hi,

the default encoding is only used when creating new files. Opening existing files detects the encoding as described above.

Can you please send me the XML file to support@textasticapp.com so I can try it here?