In my opinion, we should preserve endangered minor languages because they are the most outstanding written and oral representation of a group of people's culture. As a matter of fact, a language always describes the way their speakers understand their environment and how they connect it to their thinking.
For example, the German word WELTSCHMERZ is the combination of der Schmerz (the pain) and die Welt (the world). It means mental depression caused by the actual state of the world ;)
Unfortunately, our aboriginal language in the Canary Islands (Guanche) became extinct some centuries ago when the conquest by the spaniards took place. I can only remember two words: tamaragua (good day) and tagoror (welcome). That's all about it. What is striking is the fact that Canarian accents are pretty different from one island to another.