I think the solution is to require new participants to use a wizard in posting a question.
This could be implemented as a web form that has more than two boxes (right now we have two -- the title field and the body), where each box is required, and there is a tiny specific help feature that pops up for each box.
What we would need to do in order to implement this would be to first come up with a list of the most common types of question, and then draft the input box prompts and help bubbles that would elicit a reasonably well posed question.
For example, for single-word-request, there would be a box for "show us the research you attempted, and include at least one link as well as an explanation of why your research left you unsatisfied." (The wording can be improved -- that was a very rough draft.) There would also be a box for the sample sentence.
There would be a link to a canonical q-a (perhaps on Meta) showing two examples of well posed questions.
At the VERY BEGINNING the participant would be asked, "Are you a beginning English learner? If so, please don't post here. There is another site made just for you! (link to ELL)"
Experienced users (above a certain rep specific to question formulation) would not be required to use the wizard, but everyone should have the option to use it.