Detect Language of NSString

You can use -requestCheckingOfString:… instead. NSTextCheckingTypeOrthography attempts to identify the language used in the string, and the completion handler receives an NSOrthography parameter that can be used to get information about the orthography in the string, including its dominant language.

The following example outputs dominant language = de:

NSSpellChecker *spellChecker = [NSSpellChecker sharedSpellChecker];
[spellChecker setAutomaticallyIdentifiesLanguages:YES];
NSString *spellCheckText = @"Guten Herr Mustermann. Dies ist ein deutscher Text. Bitte löschen Sie diesen nicht.";

[spellChecker requestCheckingOfString:spellCheckText
    range:(NSRange){0, [spellCheckText length]}
    types:NSTextCheckingTypeOrthography
    options:nil
    inSpellDocumentWithTag:0
    completionHandler:^(NSInteger sequenceNumber, NSArray *results, NSOrthography *orthography, NSInteger wordCount) {
        NSLog(@"dominant language = %@", orthography.dominantLanguage);
}];

There is API in cocoa available to check the language of a string, and it is always best to use Foundation over CoreFoundation whenever possible.

NSArray *tagschemes = [NSArray arrayWithObjects:NSLinguisticTagSchemeLanguage, nil];
NSLinguisticTagger *tagger = [[NSLinguisticTagger alloc] initWithTagSchemes:tagschemes options:0];
[tagger setString:@"Das ist ein bisschen deutscher Text. Bitte löschen Sie diesen nicht."];
NSString *language = [tagger tagAtIndex:0 scheme:NSLinguisticTagSchemeLanguage tokenRange:NULL sentenceRange:NULL];

Alternatively, if you happen to have mixed language text, you can use the enumerateLinguisticTagsInRange API to get the language of each word in the text.

Thats the result:

- (NSString *)languageForString:(NSString *) text{

     if (text.length < 100) {
         return (NSString *) CFStringTokenizerCopyBestStringLanguage((CFStringRef)text, CFRangeMake(0, text.length));
     } else {
         return (NSString *)CFStringTokenizerCopyBestStringLanguage((CFStringRef)text, CFRangeMake(0, 100));
     }
}