In order to be able to get contributors exercices, we need to have a toll on server side to enter exercices.
A possible way would be to have a text editor allowing contributors to enter exercices similar to what is done in a wiki.
Lets take the example of a multiple choice question sentence where dots ....... have to be filled by an answer.
Here is the sentence:
"I have seen a red ....... squirrel ....... in a tree."
Here is what it should be filled with
"I have seen a red .adjective. squirrel .name. in a tree."
Here is what the exercice creator would enter.
"I have seen a [red|*name|adjective] [squirrel|*name|adjective] in a tree."
There should a way to be able to test in real time if the syntax of the sentences are valid or if the exercice reach the goal thought by the creator.