There is an "official" SE answer to this:
Focus on questions about an actual problem you have faced. Include details about what you have tried and exactly what you are trying to do.
This wording has been around as long as SO has existed (as far as I know) and is currently the second item on the Tour (under the Help menu).
Although non-technical SE sites like this one aren't so much about problems, it's still applicable:
- Be clear about what you're asking
- If you think you know the answer or part of it, say so and ask for more clarification about whatever part you don't understand.
- If you leave out things you know about the answer (or that you're pretty sure you know), then you're making the question less clear, and less useful.
I've found that almost every question that says something like: "The answer should include blah blah blah..." deserves a downvote because it's clear why the OP is focussing on that aspect.
e.g. in your example, "Do Protestants have a liturgical language?" is probably too broad, since it doesn't seem like all or most protestants do. Something like the following would be better:
"Do any Protestant groups have a liturgical language? I think that the High German used by groups such as the Amish would qualify because most don't speak it amongst themselves."