LCes dernières années l'extinction de, la biodiversité linguistique s'est complèment accrubeaucoup/énormément/fortement reduite.

The "BIOdiversité" is the diversity of life forms (bios = life in Greek)
"Extinction" is the complete disappearance of something, so it doesn't make sense to say it has increased. It's like saying that the absence of something has diminished