Index: lib/redmine/i18n.rb
===================================================================
--- lib/redmine/i18n.rb	(revision 21772)
+++ lib/redmine/i18n.rb	(working copy)
@@ -95,7 +95,7 @@
         m = ((hours - h) * 60).round
         "%d:%02d" % [h, m]
       else
-        "%.2f" % hours.to_f
+        sprintf("%.2f", hours.to_f).gsub('.', l(:"number.format.separator"))
       end
     end
 
Index: test/helpers/application_helper_test.rb
===================================================================
--- test/helpers/application_helper_test.rb	(revision 21772)
+++ test/helpers/application_helper_test.rb	(working copy)
@@ -2152,9 +2152,10 @@
       assert_equal '0:45 hour', l_hours(0.75)
     end
     with_settings :timespan_format => 'decimal' do
-      assert_equal '0.75', format_hours(0.75)
-      assert_equal '0.75 h', l_hours_short(0.75)
-      assert_equal '0.75 hour', l_hours(0.75)
+      time = '0.75'.gsub('.', l(:"number.format.separator"))
+      assert_equal time, format_hours(0.75)
+      assert_equal "#{time} h", l_hours_short(0.75)
+      assert_equal "#{time} hour", l_hours(0.75)
     end
   end