3 files changed, 14 insertions, 8 deletions
diff --git a/activesupport/lib/active_support/core_ext/array/conversions.rb b/activesupport/lib/active_support/core_ext/array/conversions.rb
index 1e0de651c7..d6ae031c0d 100644
--- a/activesupport/lib/active_support/core_ext/array/conversions.rb
+++ b/activesupport/lib/active_support/core_ext/array/conversions.rb
@@ -1,6 +1,5 @@
 require 'active_support/xml_mini'
 require 'active_support/core_ext/hash/keys'
-require 'active_support/core_ext/hash/reverse_merge'
 require 'active_support/core_ext/string/inflections'
 
 class Array
@@ -62,14 +61,10 @@ class Array
       :last_word_connector => ', and '
     }
     if defined?(I18n)
-      namespace = 'support.array.'
-      default_connectors.each_key do |name|
-        i18n_key = (namespace + name.to_s).to_sym
-        default_connectors[name] = I18n.translate i18n_key, :locale => options[:locale]
-      end
+      i18n_connectors = I18n.translate(:'support.array', locale: options[:locale], default: {})
+      default_connectors.merge!(i18n_connectors)
     end
-
-    options.reverse_merge! default_connectors
+    options = default_connectors.merge!(options)
 
     case length
     when 0
diff --git a/activesupport/test/core_ext/array_ext_test.rb b/activesupport/test/core_ext/array_ext_test.rb
index 58835c0ac5..9dfa2cbf11 100644
--- a/activesupport/test/core_ext/array_ext_test.rb
+++ b/activesupport/test/core_ext/array_ext_test.rb
@@ -90,6 +90,12 @@ class ArrayExtToSentenceTests < ActiveSupport::TestCase
   def test_one_non_string_element
     assert_equal '1', [1].to_sentence
   end
+
+  def test_does_not_modify_given_hash
+    options = { words_connector: ' ' }
+    assert_equal "one two, and three", ['one', 'two', 'three'].to_sentence(options)
+    assert_equal({ words_connector: ' ' }, options)
+  end
 end
 
 class ArrayExtToSTests < ActiveSupport::TestCase
diff --git a/activesupport/test/i18n_test.rb b/activesupport/test/i18n_test.rb
index 4f2027f4eb..ddbba444cf 100644
--- a/activesupport/test/i18n_test.rb
+++ b/activesupport/test/i18n_test.rb
@@ -97,4 +97,9 @@ class I18nTest < ActiveSupport::TestCase
     I18n.backend.store_translations 'en', :support => { :array => { :two_words_connector => default_two_words_connector } }
     I18n.backend.store_translations 'en', :support => { :array => { :last_word_connector => default_last_word_connector } }
   end
+
+  def test_to_sentence_with_empty_i18n_store
+    I18n.backend.store_translations 'empty', {}
+    assert_equal 'a, b, and c', %w[a b c].to_sentence(locale: 'empty')
+  end
 end