Fixed -- Fixed docs build on Sphinx 5+.
Empty language is not supported anymore.
@@ -9,6 +9,11 @@ PAPER ?=
BUILDDIR ?= _build
LANGUAGE ?=
+# Set the default language.
+ifndef LANGUAGE
+override LANGUAGE = en
+endif
+
# Convert something like "en_US" to "en", because Sphinx does not recognize
# underscores. Country codes should be passed using a dash, e.g. "pt-BR".
LANGUAGEOPT = $(firstword $(subst _, ,$(LANGUAGE)))
