diff --git a/api/v01/entities/vrp_input.rb b/api/v01/entities/vrp_input.rb
index 2f3dbf1ab..3597e49d5 100644
--- a/api/v01/entities/vrp_input.rb
+++ b/api/v01/entities/vrp_input.rb
@@ -200,6 +200,7 @@ module VrpConfiguration
     optional(:geometry_polyline, type: Boolean, documentation: { hidden: true }, desc: '[DEPRECATED] Use geometry instead, with :polylines or :encoded_polylines')
     optional(:intermediate_solutions, type: Boolean, desc: 'Return intermediate solutions if available')
     optional(:csv, type: Boolean, desc: 'The output is a CSV file if you do not specify api format')
+    optional(:use_deprecated_csv_headers, type: Boolean, desc: 'Forces API to ignore provided language to return old CSV headers')
     optional(:allow_empty_result, type: Boolean, desc: 'Allow no solution from the solver used')
   end
 
diff --git a/lib/helper.rb b/lib/helper.rb
index 79dd6714c..0556ae638 100644
--- a/lib/helper.rb
+++ b/lib/helper.rb
@@ -65,19 +65,21 @@ def self.euclidean_distance(loc_a, loc_b)
 
   def self.merge_results(results, merge_unassigned = true)
     results.flatten!
+    results.compact!
     {
-      solvers: results.flat_map{ |r| r && r[:solvers] }.compact,
-      cost: results.map{ |r| r && r[:cost] }.compact.reduce(&:+),
-      cost_details: results.map{ |r| r && r[:cost_details] }.compact.sum,
-      iterations: (results.size != 1) ? nil : results[0] && results[0][:iterations],
-      heuristic_synthesis: (results.size != 1) ? nil : results[0] && results[0][:heuristic_synthesis],
-      routes: results.flat_map{ |r| r && r[:routes] }.compact.uniq,
-      unassigned: merge_unassigned ? results.flat_map{ |r| r && r[:unassigned] }.compact.uniq : results.map{ |r| r && r[:unassigned] }.compact.last,
-      elapsed: results.map{ |r| r && r[:elapsed] || 0 }.reduce(&:+),
-      total_time: results.map{ |r| r && r[:total_time] }.compact.reduce(&:+),
-      total_travel_time: results.map{ |r| r && r[:total_travel_time] }.compact.reduce(&:+),
-      total_value: results.map{ |r| r && r[:total_travel_value] }.compact.reduce(&:+),
-      total_distance: results.map{ |r| r && r[:total_distance] }.compact.reduce(&:+)
+      solvers: results.flat_map{ |r| r[:solvers] }.compact,
+      cost: results.map{ |r| r[:cost] }.compact.reduce(&:+),
+      cost_details: results.map{ |r| r[:cost_details] }.compact.sum,
+      iterations: results.size != 1 ? nil : results[0][:iterations],
+      heuristic_synthesis: results.size != 1 ? nil : results[0][:heuristic_synthesis],
+      routes: results.flat_map{ |r| r[:routes] }.compact.uniq,
+      unassigned: merge_unassigned ? results.flat_map{ |r| r[:unassigned] }.compact.uniq : results.map{ |r| r[:unassigned] }.compact.last,
+      elapsed: results.map{ |r| r[:elapsed] || 0 }.reduce(&:+),
+      total_time: results.map{ |r| r[:total_time] }.compact.reduce(&:+),
+      total_travel_time: results.map{ |r| r[:total_travel_time] }.compact.reduce(&:+),
+      total_value: results.map{ |r| r[:total_travel_value] }.compact.reduce(&:+),
+      total_distance: results.map{ |r| r[:total_distance] }.compact.reduce(&:+),
+      use_deprecated_csv_headers: results.any?{ |r| r[:use_deprecated_csv_headers] },
     }
   end
 
diff --git a/lib/output_helper.rb b/lib/output_helper.rb
index 288d0b5b2..34458eee9 100644
--- a/lib/output_helper.rb
+++ b/lib/output_helper.rb
@@ -208,6 +208,7 @@ def self.formatted_duration(duration)
     def self.build_csv(solutions)
       return unless solutions
 
+      I18n.locale = :legacy if solutions.any?{ |s| s[:use_deprecated_csv_headers] }
       header, unit_ids, max_timewindows_size, scheduling, any_unassigned = generate_header(solutions)
 
       CSV.generate{ |output_csv|
diff --git a/models/configuration.rb b/models/configuration.rb
index 9bd462dfa..cfc17a04d 100644
--- a/models/configuration.rb
+++ b/models/configuration.rb
@@ -79,6 +79,7 @@ class Restitution < Base
     field :geometry, default: []
     field :intermediate_solutions, default: true
     field :csv, default: false
+    field :use_deprecated_csv_headers, default: false
     field :allow_empty_result, default: false
   end
 
diff --git a/models/vrp.rb b/models/vrp.rb
index 533485895..d054dad6d 100644
--- a/models/vrp.rb
+++ b/models/vrp.rb
@@ -79,6 +79,7 @@ class Vrp < Base
     field :restitution_geometry, default: []
     field :restitution_intermediate_solutions, default: true
     field :restitution_csv, default: false
+    field :restitution_use_deprecated_csv_headers, default: false
     field :restitution_allow_empty_result, default: false
 
     field :schedule_range_indices, default: nil # extends schedule_range_date
@@ -462,6 +463,7 @@ def restitution=(restitution)
       self.restitution_geometry = restitution[:geometry]
       self.restitution_intermediate_solutions = restitution[:intermediate_solutions]
       self.restitution_csv = restitution[:csv]
+      self.restitution_use_deprecated_csv_headers = restitution[:use_deprecated_csv_headers]
       self.restitution_allow_empty_result = restitution[:allow_empty_result]
     end
 
diff --git a/optimizer_wrapper.rb b/optimizer_wrapper.rb
index 634e423a4..58a4e5cc7 100644
--- a/optimizer_wrapper.rb
+++ b/optimizer_wrapper.rb
@@ -190,6 +190,7 @@ def self.define_process(service_vrp, job = nil, &block)
     check_result_consistency(expected_activity_count, result) if service_vrp[:service] != :demo # demo solver returns a fixed solution
 
     log "<-- define_process levels (dicho: #{dicho_level}, split: #{split_level}) elapsed: #{(Time.now - tic).round(2)} sec", level: :info
+    result[:use_deprecated_csv_headers] = vrp.restitution_use_deprecated_csv_headers
     result
   end
 
diff --git a/test/api/v01/output_test.rb b/test/api/v01/output_test.rb
index 23eae9f01..20f234425 100644
--- a/test/api/v01/output_test.rb
+++ b/test/api/v01/output_test.rb
@@ -275,6 +275,18 @@ def test_provided_language
         submit_csv api_key: 'demo', vrp: vrp, http_accept_language: provided
       end
     }
+
+    [true, false].each{ |parameter_value|
+      vrp[:configuration][:restitution][:use_deprecated_csv_headers] = parameter_value
+      OutputHelper::Result.stub(
+        :build_csv,
+        lambda { |solutions|
+          assert_equal parameter_value, solutions.first[:use_deprecated_csv_headers]
+        }
+      ) do
+        submit_csv api_key: 'demo', vrp: vrp, http_accept_language: 'fr'
+      end
+    }
   end
 
   def test_returned_types
@@ -478,7 +490,7 @@ def test_csv_headers_compatible_with_import_according_to_language
            'duration per destination', 'visit duration', 'tags visit', 'tags', 'quantity[kg]',
            'time window start 1', 'time window end 1', 'vehicle', 'reference'],
       es: [
-        'nombre del plan', 'referencia del plan', 'gira', 'nombre', 'tipo parada', 'lat', 'lng', 'hora', 'fin',
+        'plan', 'referencia del plan', 'gira', 'nombre', 'tipo parada', 'lat', 'lng', 'hora', 'fin',
         'horario inicio 1', 'horario fin 1', 'duración de preparación', 'duración visita', 'cantidad[kg]',
         'etiquetas visita', 'etiquetas', 'vehículo', 'referencia visita'],
       fr: ['plan', 'référence plan', 'tournée', 'nom', 'lat', 'lng', 'type arrêt', 'heure',
@@ -497,4 +509,26 @@ def test_csv_headers_compatible_with_import_according_to_language
       }
     end
   end
+
+  def test_use_deprecated_csv_headers_asynchronously
+    vrp = VRP.lat_lon
+    vrp[:configuration][:restitution] = { csv: true }
+
+    legacy_basic_headers = %w[vehicle_id id point_id type begin_time end_time setup_duration duration skills]
+    french_basic_headers = ['tournée', 'référence', 'heure', 'fin de la mission', 'durée client', 'durée visite', 'libellés']
+    [[true, legacy_basic_headers],
+     [false, french_basic_headers]].each{ |parameter, expected|
+
+      vrp[:configuration][:restitution][:use_deprecated_csv_headers] = parameter
+
+      asynchronously start_worker: true do
+        @job_id = submit_csv api_key: 'demo', vrp: vrp, http_accept_language: 'fr'
+        wait_status_csv @job_id, 200, api_key: 'demo', http_accept_language: 'fr'
+        current_headers = last_response.body.split("\n").first.split(',')
+        assert_empty expected - current_headers
+
+        delete_completed_job @job_id, api_key: 'ortools'
+      end
+    }
+  end
 end