You cannot think without a language. Every action of the mind is created with a form of a language. It follows that the greater control and knowledge of language you possess, the better you will be able to think.
Furthermore, if you are able to spread that language, you will be more powerful. Your ideas will be understood and have a greater chance of being accepted widely. Language = Power. When Europeans sought to colonize the world in order to gain wealth and prestige, they brought their language with them to the “new world.” The wanted to colonize the mind of the “savages.” By taking away their language and replacing it with English, French, Spanish, German, etc. they make the natives appropriate their culture. The colonists were able to gain control of the thoughts of an entire culture and make it their own. Every action of the mind, became whitened.
“Among a group of young Antilleans, he who can express himself, who masters the language, is the one to look out for: be wary of him; he’s almost white.” – Fanon pg. 4
“To speak a language is to appropriate its world and culture.” – Fanon pg. 21
The colonial act of eliminating the native language created an identity crisis for the native cultures. They could no longer think naturally, because every thought was controlled by the colonial influences. In Fanon’s book, he not only critiques the colonial language, but he also critiques the idea of reason. Not only did the Europeans push language, they also demanded reason. Fanon argues that reason is a western creation, not something inherent to non-European culture.
“There is a sort of impassioned imperialism of reason: for he wishes not only to convince others that he is right; his goal is to persuade them that there is an absolute and unconditioned value to rationalism. – Satre pg 98
“Emotion is Negro as reason is Greek.” – Fanon pg 106
He sees reason as something that creates barriers and divides. Because of it, “silence is everywhere.” (pg. 107)
“I find myself, me. a man, in a world where words are fringed with silence; in a world where the other hardens endlessly.” – Fanon pg. 203
Maybe the solution to this silence is to create a society based off of “internal kinship” (pg. 92). But this kinship would come through a form of “black identity” and Fanon is opposed to that idea.
Ultimately, his call to action is to “demand human behavior from the other.” and “never to let decisions renounce my freedom.” (pg. 204)
Greg's Arts One Blog 
Interesting. Though I think that Fanon doesn’t really reject European reason (or, for that matter, European language). He’s happy to draw on thinkers such as Hegel, Sartre, Freud, and Lacan, though he points out they may have to be modified when we take account of the colonial context in somewhere like Martinique.