Ilzach Elvish

Elves are crazy, for a variety of reasons. Within this, there are certain subsets who are particularly notorious. The Ilzach Elves nearly brought down a country with their language, thus giving a more literal argument against the phrase "Sticks and stones may break my bones, but words will never hurt me." The language was obliterated sometime around the 1900s.

A Brief Introduction

Ilzachish was not a natural language. It was very deliberately derived from Elvish, and used that alphabet. According to records, the elves who spoke it claimed that their plan was to use it to conquer the world. The elves who did not speak it recorded that the Ilzach Elves designed the language as an elitist snub against their enemies, an attempt to create would be the perfect language.
Since it has not been spoken in four centuries, we are not currently sure precisely why it was so unpleasant. Some records mention shrill sounds and dissonant tones. Others write of an overly elaborate verb system and a series of prepositions that didn't actually mean anything. As a constructed language, the dictionary was supposedly rather incomplete, lacking several crucial words needed to successfully communicate.

And Then They Attempted Mass Murder

At some point, the Ilzachians discovered that when sung in a choir, their language could shatter metal. With this discovery, they began planning a massive attack against Paratorion, the country known for its robots and focus on the technological side of things. Ergo, using a lot of metal in their construction habits.
The Ilzachians were nigh unstoppable. A number of Paratorion's floating cities were brought down from the sky, resulting in the loss of thousands of lives.
As a nation that typically eschewed the use of magic, Paratorion was entirely unprepared for such an open assault. Even when they turned to the magic of their allies, it was not enough. No mage or sorceress they brought it was able to find a counter to the destruction of Ilzachish choir. And since it was a language of supposed elites, they couldn't even do proper reconnaissance since no one else understood the words.

Bespelled

A solution was finally discovered by the mage Janek McKibbin. His solution was to craft a spell to banish the Ilzachish language. There were a number of components to the spell, and challenges to overcome, but Janek completed his work before the Ilzachian elves could reach the Paratorian capital.
There was a magnificent showdown between the mage and the choir. In the end, they were too arrogant to consider that he might actually be capable of doing what he said he could. So he did it, and their forces were thrown into chaos.
The spell caused a small amount of damage to their brains as it stripped the knowledge of the language from them. The Ilzachians were of course the most affected, since it was their entire language, but those who had fought them also suffered some damage as they'd picked up a few words by exposure.
The Ilzach elvish clan was essentially eliminated when they lost their language. It is a shame, but also difficult to regret the loss of such a ridiculous language.