diff --git a/activesupport/lib/active_support/duration.rb b/activesupport/lib/active_support/duration.rb
index 2818b8d68b..5a64fc52cc 100644
--- a/activesupport/lib/active_support/duration.rb
+++ b/activesupport/lib/active_support/duration.rb
@@ -91,7 +91,7 @@ module ActiveSupport
         reduce(::Hash.new(0)) { |h,(l,r)| h[l] += r; h }.
         sort_by {|unit,  _ | [:years, :months, :days, :minutes, :seconds].index(unit)}.
         map     {|unit, val| "#{val} #{val == 1 ? unit.to_s.chop : unit.to_s}"}.
-        to_sentence(:locale => :en)
+        to_sentence(locale: ::I18n.default_locale)
     end
 
     def as_json(options = nil) #:nodoc:
diff --git a/activesupport/test/core_ext/duration_test.rb b/activesupport/test/core_ext/duration_test.rb
index 2b893c7cd0..c283b546e6 100644
--- a/activesupport/test/core_ext/duration_test.rb
+++ b/activesupport/test/core_ext/duration_test.rb
@@ -70,6 +70,15 @@ class DurationTest < ActiveSupport::TestCase
     assert_equal '14 days',                         1.fortnight.inspect
   end
 
+  def test_inspect_locale
+    current_locale = I18n.default_locale
+    I18n.default_locale = :de
+    I18n.backend.store_translations(:de, { support: { array: { last_word_connector: ' und ' } } })
+    assert_equal '10 years, 1 month und 1 day', (10.years + 1.month  + 1.day).inspect
+  ensure
+    I18n.default_locale = current_locale
+  end
+
   def test_minus_with_duration_does_not_break_subtraction_of_date_from_date
     assert_nothing_raised { Date.today - Date.today }
   end