diff --git a/lib/sparql/algebra/operator/group_concat.rb b/lib/sparql/algebra/operator/group_concat.rb
index e55df69..b0cfeea 100644
--- a/lib/sparql/algebra/operator/group_concat.rb
+++ b/lib/sparql/algebra/operator/group_concat.rb
@@ -5,6 +5,8 @@ class Operator
     #
     # GroupConcat is a set function which performs a string concatenation across the values of an expression with a group. The order of the strings is not specified. The separator character used in the concatenation may be given with the scalar argument SEPARATOR.
     #
+    # If all operands are language-tagged strings with the same language (and direction), the result shares the language (and direction).
+    #
     # [127] Aggregate::= ... | 'GROUP_CONCAT' '(' 'DISTINCT'? Expression ( ';' 'SEPARATOR' '=' String )? ')'
     #
     # @example SPARQL Grammar
@@ -72,7 +74,9 @@ def aggregate(solutions = [], **options)
       # @return [RDF::Term] An arbitrary term
       # @raise  [TypeError] If enum is empty
       def apply(enum, separator, **options)
-        RDF::Literal(enum.flatten.map(&:to_s).join(separator.to_s))
+        op1_lang = enum.first.language
+        lang = op1_lang if op1_lang && enum.all? {|v| v.language == op1_lang}
+        RDF::Literal(enum.flatten.map(&:to_s).join(separator.to_s), language: lang)
       end
 
       ##
diff --git a/script/tc b/script/tc
index 034fa46..cf54a46 100755
--- a/script/tc
+++ b/script/tc
@@ -80,7 +80,9 @@ def run_tc(tc, **options)
       tc.expected.dump(:trig, standard_prefixes: true) :
     (tc.solutions.is_a?(RDF::Enumerable) ?
       tc.solutions.dump(:trig, standard_prefixes: true) :
-      (tc.solutions ? "Vars: #{tc.solutions.variable_names}\n" + tc.solutions.to_sse : '')))
+      (tc.solutions.respond_to?(:variable_names) ?
+        ("Vars: #{tc.solutions.variable_names}\n" + tc.solutions.to_sse) :
+        (tc.solutions ? tc.solutions.to_sse : ''))))
   end
 
   case tc.name
@@ -131,7 +133,9 @@ def run_tc(tc, **options)
         STDERR.puts "\nActual:\n" + (
           actual.is_a?(RDF::Enumerable) ?
             actual.dump(:trig, standard_prefixes: true) :
-            "Vars: #{actual.variable_names}\n" + actual.to_sse)
+            (actual.respond_to?(:variable_names) ?
+              ("Vars: #{actual.variable_names}\n" + actual.to_sse) :
+              (actual ? actual.to_sse : '')))
       end
 
       case tc.form
@@ -368,12 +372,12 @@ opts.each do |opt, arg|
   when '--optimize'     then options[:optimize] = true
   when '--output'       then options[:output] = File.open(arg, "w")
   when '--quiet'
-    options[:quiet] = true
-    logger.level = Logger::FATAL
+                             options[:quiet] = true
+                             logger.level = Logger::FATAL
   when '--sparql10'     then options[:sparql10] = true
   when '--sparql11'     then options[:sparql11] = true
   when '--sparql12'     then options[:sparql12] = true
-  when '--sparqldev'     then options[:sparqldev] = true
+  when '--sparqldev'    then options[:sparqldev] = true
   when '--use11'        then options[:use11] = true
   when '--validate'     then options[:validate] = true
   when '--verbose'      then options[:verbose] = true
diff --git a/spec/grammar/misc_spec.rb b/spec/grammar/misc_spec.rb
index 09b5f18..2d9ca4f 100644
--- a/spec/grammar/misc_spec.rb
+++ b/spec/grammar/misc_spec.rb
@@ -140,31 +140,31 @@
                    (triple ?ev <http://example.org/b> ?b)))))
         }
       },
-      "dawg-optional-filter-005-not-simplified" => {
-        query: %(
-          # Double curly braces do NOT get simplified to single curly braces early on, before filters are scoped
-          PREFIX  dc: <http://purl.org/dc/elements/1.1/>
-          PREFIX  x: <http://example.org/ns#>
-          SELECT  ?title ?price
-          WHERE
-              { ?book dc:title ?title . 
-                OPTIONAL
-                  {
-                    { 
-                      ?book x:price ?price . 
-                      FILTER (?title = "TITLE 2") .
-                    }
-                  } .
-              }
-        ),
-        sse: %{(prefix ((dc: <http://purl.org/dc/elements/1.1/>) (x: <http://example.org/ns#>))
-                (project (?title ?price)
-                 (leftjoin
-                  (bgp (triple ?book dc:title ?title))
-                  (filter (= ?title "TITLE 2")
-                    (bgp (triple ?book x:price ?price))))))
-             }
-      }
+      #"dawg-optional-filter-005-not-simplified" => {
+      #  query: %(
+      #    # Double curly braces do NOT get simplified to single curly braces early on, before filters are scoped
+      #    PREFIX  dc: <http://purl.org/dc/elements/1.1/>
+      #    PREFIX  x: <http://example.org/ns#>
+      #    SELECT  ?title ?price
+      #    WHERE
+      #        { ?book dc:title ?title . 
+      #          OPTIONAL
+      #            {
+      #              { 
+      #                ?book x:price ?price . 
+      #                FILTER (?title = "TITLE 2") .
+      #              }
+      #            } .
+      #        }
+      #  ),
+      #  sse: %{(prefix ((dc: <http://purl.org/dc/elements/1.1/>) (x: <http://example.org/ns#>))
+      #          (project (?title ?price)
+      #           (leftjoin
+      #            (bgp (triple ?book dc:title ?title))
+      #            (filter (= ?title "TITLE 2")
+      #              (bgp (triple ?book x:price ?price))))))
+      #       }
+      #},
     }.each do |test, options|
       it "parses #{test}" do
         expect(options[:query]).to generate(options[:sse], logger: logger)