fix doc build - english as default

Author: RonnyPfannschmidt

docs/conf.py

@@ -33,7 +33,7 @@
 version = ".".join(release.split(".")[:2])
 
 
-language = None
+language = 'en'
 
 pygments_style = "sphinx"
 # html_logo = "_static/img/plug.png"