Based on Larme's tip, THe answer was pretty simple ! for all of the future encounters of this problem, use the following code :
NSRange nameRange = [author.name rangeOfString:text options:NSAnchoredSearch | NSDiacriticInsensitiveSearch];
NSRange descriptionRange = [author.genre rangeOfString:text options:NSAnchoredSearch | NSDiacriticInsensitiveSearch];