We present the crowdsourcing platform Donnez Votre Français à la Science (DFS, or “Give your French to Science”), which aims to collect linguistic data and document language use, with a special focus on regional variation in European French. The activities not only gather data that is useful for scientific studies, but they also provide feedback to the general public; this is important in order to reward participants, to encourage them to follow future surveys, and to foster interaction with the scientific community. The two main activities described here are 1) a linguistic survey on lexical variation with immediate feedback and 2) a speaker geolocalisation system; i.e., a quiz that guesses the linguistic origin of the participant by comparing their answers with previously gathered linguistic data. For the geolocalisation activity, we set up a simulation framework to optimise predictions. Three classification algorithms are compared: the first one uses clustering and shibboleth detection, whereas the other two rely on feature elimination techniques with support Vector Machines and Maximum Entropy models as underlying base classifiers. The best-performing system uses a selection of 17 questions and reaches a localisation accuracy of 66%, extending the prediction from the one-best area (one among 109 base areas) to its first-order and second-order neighbouring areas.