Ok so problem solved after some hours of googling…
There was actually two bugs in my code. The first one was a file encoding error and the second was the problem with the MySQL Data base configuration.
First, to solve the error caused by MySQL I used this two articles :
http://www.dotkam.com/2008/09/14/configure-rails-and-mysql-to-support-utf-8/
http://www.rorra.com.ar/2010/07/30/rails-3-mysql-and-utf-8/
Second, to solve the file encoding problem I added these 2 lines in my config/environment.rb
Encoding.default_external = Encoding::UTF_8
Encoding.default_internal = Encoding::UTF_8
Hopefully this will help someone 🙂