The Conference of Computational Linguistics Students—the acronym makes sense in German—is an opportunity for Colis from all over the German-speaking world to meet other students, exchange ideas and explore a new city. Other Colis, or maybe even you, give lectures about their Coli projects.
More information, including when the next TaCoS will take place, can be found on this website.
By the way, TaCoS 2016 took place in Heidelberg, and TaCoS 2020 almost did too. If you think there should be another TaCoS in Heidelberg, just suggest it at a student council meeting 😉.