This adds a formatter for plurals that works for all locales.

chrome/common/plural_formatter.h

Index: chrome/common/plural_formatter.h
diff --git a/chrome/common/plural_formatter.h b/chrome/common/plural_formatter.h
new file mode 100644
index 0000000000000000000000000000000000000000..ef0c5023d4064481f8fa13324e3934b5d5acfa87
--- /dev/null
+++ b/chrome/common/plural_formatter.h
@@ -0,0 +1,105 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_COMMON_PLURAL_FORMATTER_H__
+#define CHROME_COMMON_PLURAL_FORMATTER_H__
+#pragma once
+
+// This file defines a method to format a plural value properly as a
+// string for multiple locales.
+
+#include <string>
+#include <vector>
+
+#include "base/gtest_prod_util.h"
+#include "base/scoped_ptr.h"
+#include "base/string16.h"
+
+class PluralFormatterImpl;
+
+// This class returns appropriate plural string for the locale:
+// e.g. singular: "Your hovercraft has 1 eel." versus plural: "Your
+// hovercraft has 42 eels."  If you never have a particular value of
+// something (e.g. if you never have "1 eel" in your hovercraft), you
+// still need to specify a message for that value: plural rules in
+// other languages are very different from English, and, for instance,
+// the ONE message may be used for all numbers ending in one, not just
+// a literal "1".
+//
+// Note that this class will ONLY format a string with zero or one
+// integer "#" fields in it.
+//
+// NOTE: See the file plural_formatter_example.grd for an example of
+// the messages you need to create to use this class.  Please use that
+// form, and don't invent your own: there's logic in there.
+//
+// For the example messages, the English strings would be "Your
+// hovercraft has 1 eel."  and "Your hovercraft has 42 eels."  Other
+// translations will be created for each other locale, based on how
+// they handle plurals.
+//
+// For cases where your string doesn't make sense (i.e. there can never
+// be zero eels in your hovercraft), you may leave out that string, and
+// pass "-1" for the message ID when creating the PluralFormatter.
+//
+// Don't expect the "few" and "many" cases to be used for English: they
+// won't be.  Only ONE and DEFAULT are used for English.
+//
+// The messages would be handed to the PluralFormatter as follows:
+//
+// ===
+// PluralFormatter formatter(IDS_EELS_ZERO,
+//                           IDS_EEL_ONE,
+//                           IDS_EELS_TWO,
+//                           IDS_EELS_FEW,
+//                           IDS_EELS_MANY,
+//                           IDS_EELS_DEFAULT);
+//
+// // Result is "Your hovercraft has 1 eel."
+// string16 result = formatter.GetPluralString(1);
+//
+// // Result is "Your hovercraft has 42 eels."
+// string16 result = formatter.GetPluralString(42);
+// ===
+//
+// When you create these strings in the main string file, please leave
+// the descriptions intact (well, obviously, change the part that says
+// "Describes the number of eels in a hovercraft."!) so that they
+// serve as a guide for the translators to help reduce translation
+// errors.
+

[Paweł Hajdan Jr., 2011/03/25 09:32:19]

nit: Remove the empty line for the class comment.

+class PluralFormatter {
+ public:
+  typedef std::string (*StringSourceFunction)(int);

[Paweł Hajdan Jr., 2011/03/25 09:32:19]

nit: Can this typedef be moved to the private part?

+
+  // There must be exactly six message ids, in increasing cardinality:
+  // zero, one, two, few, many, default.
+  explicit PluralFormatter(const int message_ids[]);

[Paweł Hajdan Jr., 2011/03/25 09:32:19]

nit: Why do we have two ctors that do the same thing? It seems like the latter
(with 6 arguments) is better, because it is a compile-time failure if the number
of arguments doesn't match. With an array, we can only check its size during
runtime, at least with the [] declaration.

+  PluralFormatter(int zero_message_id,
+                  int one_message_id,
+                  int two_message_id,
+                  int few_message_id,
+                  int many_message_id,
+                  int default_message_id);
+  ~PluralFormatter();
+
+  string16 GetPluralString(int number);
+ private:

[Paweł Hajdan Jr., 2011/03/25 09:32:19]

nit: Add empty line above.

+  // The tests use SetStringSource(), SetOverrideLocale()
+  friend class PluralFormatterTest;
+  FRIEND_TEST_ALL_PREFIXES(PluralFormatterTest, Basic);
+  FRIEND_TEST_ALL_PREFIXES(PluralFormatterTest, TestLocales);
+
+  // Used by unit test to override resource string fetching function.
+  static void SetStringSource(StringSourceFunction string_source);
+
+  // Used by unit test to cycle through locales.  Set to NULL to reset
+  // to default.  Must be set before creating the PluralFormatter
+  // object that will use it.
+  static void SetOverrideLocale(const char* override_locale);
+
+  PluralFormatterImpl* impl_;

[Paweł Hajdan Jr., 2011/03/25 09:32:19]

Why not just scoped_ptr?

+};
+
+#endif  // CHROME_COMMON_PLURAL_FORMATTER_H__