Sorry I'm a little late for this discussion - came across it randomly in a Google search.
The term 'non-derogable' is generally used in a legal context to stipulate those rights specified in a treaty that states cannot violate under any circumstances. These differ from derogable rights. In the practice of international human rights law, any state can formally file a notice of derogation from a human rights treaty during a state of emergency. This is a public statement to the effect that they are no longer protecting the rights under particular clauses of the treaty in question. Britain did this in 2001, for instance, derogating from clauses in the European Convention on Human Rights, allowing them to implement certain anti-terrorism measures.
However, there are certain rights that are considered to be 'non-derogable,' meaning that states have no legal basis, even in a state of emergency, to refuse to honour these rights. The right to life and rights protecting against torture generally fall within this category in most international human rights treaties and as part of customary international law, although others can be included depending on the treaty in question.
Although I know this doesn't help directly in translation, I'm hoping it will give the sense of what a non-derogable right is because it is slightly different from an 'inalienable right' that others have suggested, which is a right than cannot be transferred or removed from a person. 'Inalienable' is more of a philosophical concept than 'non-derogable,' which is more of a legal concept.
Hope this helps!