Hi Luc, I've not come across your request for a student version of Terragen Sky, and I check educational license requests and support tickets on a daily basis.
Planetside Software offers educational licenses for Terragen 4 Professional including Terragen Sky Early Access, to schools, teachers and students. Here's the link to apply for an educational license as an individual or on behalf of your educational institution.
https://planetside.co.uk/educational-license-program/Please feel free to submit an application via the link above or email us at
registrations@planetside.co.uk and we'll get you set up.