Even simpler: delete “By ... own willing” from the phrase in the question, and end with “One can choose to do a particular thing.”  For example, “Did you choose to take that French course?”

In some situations, where freedom of choice might be assumed to be obvious, this might be interpreted to mean, “Did you _do_ that particular thing?”  For example, “Did you choose to have wine with dinner?”  To place the emphasis on the elective aspect of the behavior, one might ask, “Did you take that French course _by choice_?”

P.S. “I have a French course” is not common usage; one would say “I have taken a French course”, “I have studied French”, or perhaps even “I have taken French.”