As its documentation notes[0], Jinja2 only processes unicode template
data (or pure ASCII, which will implicitly decode to unicode).
The scaffolding system would read raw scaffolding data in memory (both
templates and passthrough non-templates), but fail to decode templates
before handing them to Jinja, blowing rendering up if templates
contained non-ascii.
Fix#11331 by always decoding templates from UTF8 before handing them
to jinja. This is backwards-compatible, ascii templates work as they
used to, non-ascii UTF8 templates now work correctly, non-ascii
non-UTF8 templates what are you doing?
[0] http://jinja.pocoo.org/docs/dev/api/#unicode