well, I noticed that you don't actually use an "unmodified version of Scintilla" and do patch some stuff in scintilla/scintilla_changes.patch so it is actually possible to add it there.
Yes, but the patch is only to remove languages we don't support, not to maintain our fork of Scintilla.
I can try getting it included in Scintilla, but... mercurial??
Same here :-)
But you can avoid the mercurial thing altogether. What I typically do when submitting patch to Scintilla is that I download the latest release tarball (Scintilla development isn't so active so there probably won't be conflicts with your code if it differs from the current master), create a git repository in it and add all files, then make my modifications, commit them, and finally git-format-patch the result and submit it as an attachment of the Sourceforge issue.