What is the meaning of "enlightenment imperative"? Some simple explanation?

See a translation

I don't think you can give a simple explanation of that. Would need to know more context to be able to say, because this sounds like it could be a very specific term from an academic paper.

Taking the words apart though, we have:

enlightenment: to gain wisdom. Not just knowledge, but the idea is like bringing light to a dark room, where the dark was your ignorance. This is a big change. Often considered spiritual.

imperative: a command. Something you must do.

Put together, it's harder to say. Either "a command to seek wisdom", it is imperative that you seek enlightening... like a call to action.

It for also mean the imperative of your enlightenment, meaning that your enlightenment requires you to do this. This would be like, you learned that something is harmful, so your enlightenment demands that you don't participate.

I strongly suspect though that this is a fancy name an author is giving to a specific idea. abd would need to know the source to say for sure. Philosophers and academics like to give their ideas names like this. "A Modest Proposal" means an idea that is simple and humble, but it's also the name of a famous paper about cannibalism.