Explicitly not support plural messages though fulfilling the interface.

CHANGES.rst

@@ -11,6 +11,10 @@ CHANGES
   their old locations in zope.component.interfaces instead of their current
   locations in zope.interface.interfaces.
 
+- Add compatibility with ``zope.i18n >= 4.7``. We fulfil the interface for
+  plural messages now, although we do not provide any implementation. This is
+  documented and raises NotImplementedError.
+
 
 4.0.0 (2017-05-25)
 ------------------

README.rst

@@ -1,2 +1,30 @@
+=============
+zope.app.i18n
+=============
+
+.. image:: https://img.shields.io/pypi/v/zope.app.i18n.svg
+        :target: https://pypi.python.org/pypi/zope.app.i18n/
+        :alt: Latest release
+
+.. image:: https://img.shields.io/pypi/pyversions/zope.app.i18n.svg
+        :target: https://pypi.org/project/zope.app.i18n/
+        :alt: Supported Python versions
+
+.. image:: https://travis-ci.org/zopefoundation/zope.app.i18n.svg?branch=master
+        :target: https://travis-ci.org/zopefoundation/zope.app.i18n
+
+.. image:: https://coveralls.io/repos/github/zopefoundation/zope.app.i18n/badge.svg?branch=master
+        :target: https://coveralls.io/github/zopefoundation/zope.app.i18n?branch=master
+
+Summary
+-------
+
 This package provides placeful persistent translation domains and
-message catalogs along with ZMI views for managing them.
+message catalogs along with ZMI views for managing them.
+
+Caveats
+-------
+
+Currently this integration does not support the feature of plural messages
+which is supported by the underlying ``zope.i18n`` library. In case you need
+this feature, please discuss this in the issue tracker in the repository.

src/zope/app/i18n/messagecatalog.py

@@ -52,10 +52,14 @@ def queryMessage(self, id, default=None):
 
     def getPluralMessage(self, singular, plural, n):
         'See `IMessageCatalog`'
+        # Plural messages are not supported yet. Please report an issue kn
+        # github in case you want to implement this feature.
         raise NotImplementedError
 
     def queryPluralMessage(self, singular, plural, n, dft1=None, dft2=None):
         'See `IMessageCatalog`'
+        # Plural messages are not supported yet. Please report an issue kn
+        # github in case you want to implement this feature.
         raise NotImplementedError
 
     def getIdentifier(self):

src/zope/app/i18n/tests/test_translationdomain.py

@@ -296,6 +296,23 @@ def test_translate(self):
                                   target_language='de'),
             'Guten Tag!')
 
+    def test_translate__2(self):
+        """It raises a NotImplementedError in case of plural messages."""
+        with self.assertRaises(NotImplementedError) as err:
+            self.trans1.translate('some text', msgid_plural="some texts")
+        with self.assertRaises(NotImplementedError) as err2:
+            self.trans1.translate('some text', default_plural="some texts")
+        with self.assertRaises(NotImplementedError) as err3:
+            self.trans1.translate('some text', number="some texts")
+
+        self.assertEqual(
+            str(err.exception), 'Plural messages are not supported yet')
+        self.assertEqual(
+            str(err2.exception), 'Plural messages are not supported yet')
+        self.assertEqual(
+            str(err3.exception), 'Plural messages are not supported yet')
+
+
 def test_suite():
     return unittest.TestSuite((
         unittest.defaultTestLoader.loadTestsFromName(__name__),

src/zope/app/i18n/translationdomain.py

@@ -67,6 +67,11 @@ def translate(self, msgid, mapping=None, context=None,
                   target_language=None, default=None, msgid_plural=None,
                   default_plural=None, number=None):
         """See interface `ITranslationDomain`"""
+        if any((default_plural, msgid_plural, number)):
+            # Plural messages are not supported yet. Please report an issue kn
+            # github in case you want to implement this feature.
+            raise NotImplementedError('Plural messages are not supported yet')
+
         if target_language is None and context is not None:
             avail_langs = self.getAvailableLanguages()
             # Let's negotiate the language to translate to. :)