bpo-28692: Deprecate using non-integer value for selecting a plural form in gettext. (#507)

diff --git a/Lib/gettext.py b/Lib/gettext.py
index 57d2c74..aa1d555 100644
--- a/Lib/gettext.py
+++ b/Lib/gettext.py
@@ -164,6 +164,10 @@
     except TypeError:
         raise TypeError('Plural value must be an integer, got %s' %
                         (n.__class__.__name__,)) from None
+    import warnings
+    warnings.warn('Plural value must be an integer, got %s' %
+                  (n.__class__.__name__,),
+                  DeprecationWarning, 4)
     return n
 
 def c2py(plural):