Avoid useless computations on iOS 9+

ios/RNI18n.m

@@ -1,3 +1,4 @@
+#import <UIKit/UIKit.h>
 #import "RNI18n.h"
 
 @implementation RNI18n
@@ -6,15 +7,23 @@ RCT_EXPORT_MODULE();
 
 - (NSDictionary *)constantsToExport {
   NSArray *preferredLanguages = [NSLocale preferredLanguages];
-  NSMutableArray *languages = [NSMutableArray array];
 
-  for (id language in preferredLanguages) {
-    [languages addObject:[language stringByReplacingOccurrencesOfString:@"_" withString:@"-"]];
+  if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 9) {
+    return @{
+      @"language": [preferredLanguages objectAtIndex:0],
+      @"languages": preferredLanguages
+    };
+  }
+
+  NSMutableArray *forcedLanguageTags = [NSMutableArray array];
+
+  for (id l in preferredLanguages) {
+    [forcedLanguageTags addObject:[l stringByReplacingOccurrencesOfString:@"_" withString:@"-"]];
   }
 
   return @{
-    @"language": [languages objectAtIndex:0],
-    @"languages": languages
+    @"language": [forcedLanguageTags objectAtIndex:0],
+    @"languages": forcedLanguageTags
   };
 }