Not specifically trying to weigh in on the overall conversation, but aren't git commands generally UTF-8?
> git commit and git commit-tree issues a warning if the commit log message given to it does not look like a valid UTF-8 string, unless you explicitly say your project uses a legacy encoding.
> git log, git show, git blame and friends look at the encoding header of a commit object, and try to re-code the log message into UTF-8 unless otherwise specified.