Use our unit name pluralization in Ruby

This code will be used for the shop front and reports.

lib/open_food_network/option_value_namer.rb

@@ -38,8 +38,7 @@ module OpenFoodNetwork
 
         else
           value = @variant.unit_value
-          unit_name = @variant.product.variant_unit_name
-          unit_name = unit_name.pluralize if value > 1
+          unit_name = pluralize(@variant.product.variant_unit_name, value)
         end
 
         value = value.to_i if value == value.to_i
@@ -72,5 +71,39 @@ module OpenFoodNetwork
 
       unit
     end
+
+    def pluralize(unit_name, count)
+      I18nUnitNames.instance.pluralize(unit_name, count)
+    end
+
+    # Provides efficient access to unit name inflections.
+    # The singleton property ensures that the init code is run once only.
+    # The OptionValueNamer is instantiated in loops.
+    class I18nUnitNames
+      include Singleton
+
+      def pluralize(unit_name, count)
+        return unit_name if count.nil?
+
+        @unit_keys ||= unit_key_lookup
+        key = @unit_keys[unit_name.downcase]
+
+        return unit_name unless key
+
+        I18n.t(key, scope: "unit_names", count: count, default: unit_name)
+      end
+
+      private
+
+      def unit_key_lookup
+        lookup = {}
+        I18n.t("unit_names").each do |key, translations|
+          translations.values.each do |translation|
+            lookup[translation.downcase] = key
+          end
+        end
+        lookup
+      end
+    end
   end
 end