Explicitly specifying environment variables in the tox configuration file seems to be a workaround, but I'd prefer to be able to change the locale tox (and its subprocesses) uses right from the command line.
Yes please! All my tox projects started failing with Python 3 because the LANG environment variable is no longer passed.
Also this makes projects using Click under Python 3 unusable.
Along a similar line to @aconrad (we work at the same company), I also took a stab though I did it by adding a --passenv command-line option so that folks can decide on their own what environment variables should be passed, and do so without changing tox.ini.