Changed language setting in conf.py properly.
# The language for content autogenerated by Sphinx. Refer to documentation
# for a list of supported languages.
-#language = None
+language = en
# There are two options for replacing |today|: either, you set today to some
# non-false value, then it is used:
# The language for content autogenerated by Sphinx. Refer to documentation
# for a list of supported languages.
-#language = None
+language = ko
# There are two options for replacing |today|: either, you set today to some
# non-false value, then it is used: