code: function localeComparator(model1, model2) {
      var a1 = model1.get(this.sortField),
          a2 = model2.get(this.sortField);
  
      if (a1 !== undefined && a1.localeCompare) {
          var result = a1.localeCompare(a2) * this.sortDir;
          if (result || !this.secondarySortField) {
              return result;
          }
          a1 = model1.get(this.secondarySortField);
          a2 = model2.get(this.secondarySortField);
          return a1.localeCompare(a2) * this.sortDir;
      }
  
      return a1 > a2 ? this.sortDir : (a1 < a2 ? -this.sortDir : 0);
  }
docs: This comparator can be used by collections that wish to support locale-based
  sorting.  The locale specifies how upper and lower case are compared.