Here is a collection of some of the test and experiment materials that have previously been used in language attrition research. What these tests are, what they measure, and how to administer them, is described in my textbook Language Attrition (CUP, 2011).
You may use these questionnaires in your research, but please include the appropriate reference. Should you be developing a version of the questionnaire in a different language than the ones provided here, it would be appreciated if you could contact me so that I can include it here for the convenience of others.
Language Attrition 