Fix tests

tox.ini

@@ -10,8 +10,8 @@ envlist = {py36,py37,py38,py39}-{tests,install},docs,install,py36-docs
 download = true
 # Make sure reading the UTF-8 from test.py works regardless of the locale used.
 setenv =
-    LANG=C
-    LC_ALL=C
+    LC_ALL=C.UTF-8
+    LANG=C.UTF-8
 # To pass arguments to py.test, use `tox [options] -- [pytest posargs]`.
 commands =
     py.test --pep8 --cache-clear -vv src/tests {posargs}