How do I filter a view for untranslated content? I have a site with many lessons in English, with the option to translate them into Japanese. There is a team of translators working to translate the lessons, but they need an easy way to see which lessons have not yet been translated.

Is there some way to filter or create a view that only shows content that has not yet been translated to a target language?
You could use the following 2 views filters 
Content: Revision translation affected (!= False)
Content: Default translation (= True)

for more details go to a more complete answer How to create a list of untranslated content in views?