Respect languages preferences on login page

Fixes #4169

UI/MainUI/SOGoRootPage.h

@@ -31,6 +31,8 @@
   NSString *cookieLogin;
 }
 
+- (NSArray *) languages;
+
 @end
 
 #endif /* SOGOROOTPAGE_H */

UI/MainUI/SOGoRootPage.m

@@ -521,6 +521,16 @@
   return item;
 }
 
+- (BOOL) hasManyLanguages
+{
+  return [[self languages] count] > 1;
+}
+
+- (NSString *) language
+{
+  return [[context resourceLookupLanguages] objectAtIndex: 0];
+}
+
 - (NSArray *) languages
 {
   return [[SOGoSystemDefaults sharedSystemDefaults] supportedLanguages];