I was in Wales the other week and this list came to mind. Something similar could be said for other languages I guess. I was at a bus stop next to a mother and child speaking German the other day and their conversation was pretty clear to me despite my very limited German (Lola was complaining that the church was old but her mother thought it was beautiful).
1. Children (slow and clear)
2. Learners (clear)
3. Second languagers (clear)
4. Public speakers, announcers (clear and often a translation to follow)
5. People from Llanelli or Bridgend
6. Native speakers who know your Welsh is limited
7. Native speakers who don't know your Welsh is limited
8. Native speakers from the Lleyn Peninsula
9. Old people or teenagers
10. Old people from the countryside (unclear and dialect words)
Bonhoeffer uses a similar phrase 'worldly Christianity'. It's J Gresham Machen that I want to line up most closely with. See his Christianity and culture here. Having done commentaries on Proverbs (Heavenly Wisdom) and Song of Songs (Heavenly Love), a matching title for Ecclesiastes would be Heavenly Worldliness. For my stance on worldliness, see 3 posts here.