diff --git a/C4/Biblio.pm b/C4/Biblio.pm
index 1b882864ed..2c7170c3c3 100644
--- a/C4/Biblio.pm
+++ b/C4/Biblio.pm
@@ -3624,6 +3624,8 @@ sub ModBiblioMarc {
 
     # deal with UNIMARC field 100 (encoding) : create it if needed & set encoding to unicode
     if ( $encoding eq "UNIMARC" ) {
+	my $defaultlanguage = C4::Context->preference("UNIMARCField100Language");
+        $defaultlanguage = "fre" if (!$defaultlanguage || length($defaultlanguage) != 3);
         my $string = $record->subfield( 100, "a" );
         if ( ($string) && ( length( $record->subfield( 100, "a" ) ) == 36 ) ) {
             my $f100 = $record->field(100);
@@ -3632,8 +3634,9 @@ sub ModBiblioMarc {
             $string = POSIX::strftime( "%Y%m%d", localtime );
             $string =~ s/\-//g;
             $string = sprintf( "%-*s", 35, $string );
+	    substr ( $string, 22, 3, $defaultlanguage);
         }
-        substr( $string, 22, 6, "frey50" );
+        substr( $string, 25, 3, "y50" );
         unless ( $record->subfield( 100, "a" ) ) {
             $record->insert_fields_ordered( MARC::Field->new( 100, "", "", "a" => $string ) );
         }
diff --git a/C4/Charset.pm b/C4/Charset.pm
index c294b36133..f8ddd63627 100644
--- a/C4/Charset.pm
+++ b/C4/Charset.pm
@@ -324,8 +324,10 @@ sub SetMarcUnicodeFlag {
         substr($leader, 9, 1) = 'a';
         $marc_record->leader($leader); 
     } elsif ($marc_flavour =~/UNIMARC/) {
+	my $defaultlanguage = C4::Context->preference("UNIMARCField100Language");
+        $defaultlanguage = "fre" if (!$defaultlanguage || length($defaultlanguage) != 3);
         my $string; 
-		my ($subflength,$encodingposition)=($marc_flavour=~/AUTH/?(21,9):(36,22));
+		my ($subflength,$encodingposition)=($marc_flavour=~/AUTH/?(21,12):(36,25));
 		$string=$marc_record->subfield( 100, "a" );
         if (defined $string && length($string)==$subflength) { 
 			$string = substr $string, 0,$subflength if (length($string)>$subflength);
@@ -333,9 +335,10 @@ sub SetMarcUnicodeFlag {
         else { 
             $string = POSIX::strftime( "%Y%m%d", localtime ); 
             $string =~ s/\-//g; 
-            $string = sprintf( "%-*s", $subflength, $string ); 
+            $string = sprintf( "%-*s", $subflength, $string );
+	    substr ( $string, ($encodingposition - 3), 3, $defaultlanguage);
         } 
-        substr( $string, $encodingposition, 8, "frey50  " ); 
+        substr( $string, $encodingposition, 3, "y50" );
         if ( $marc_record->subfield( 100, "a" ) ) { 
 			$marc_record->field('100')->update(a=>$string);
 		}
@@ -343,7 +346,7 @@ sub SetMarcUnicodeFlag {
             $marc_record->insert_grouped_field( 
                 MARC::Field->new( 100, '', '', "a" => $string ) ); 
         }
-		$debug && warn "encodage: ", substr( $marc_record->subfield(100, 'a'), $encodingposition, 8 );
+		$debug && warn "encodage: ", substr( $marc_record->subfield(100, 'a'), $encodingposition, 3 );
     } else {
         warn "Unrecognized marcflavour: $marc_flavour";
     }
diff --git a/cataloguing/value_builder/unimarc_field_100.pl b/cataloguing/value_builder/unimarc_field_100.pl
index 0d01554458..0ecf8443be 100755
--- a/cataloguing/value_builder/unimarc_field_100.pl
+++ b/cataloguing/value_builder/unimarc_field_100.pl
@@ -82,6 +82,9 @@ sub plugin {
 
     my $dbh = C4::Context->dbh;
 
+    my $defaultlanguage = C4::Context->preference("UNIMARCField100Language");
+    $defaultlanguage = "fre" if (!$defaultlanguage || length($defaultlanguage) != 3);
+
     my ( $template, $loggedinuser, $cookie ) = get_template_and_user(
         {
             template_name => "cataloguing/value_builder/unimarc_field_100.tmpl",
@@ -92,7 +95,7 @@ sub plugin {
             debug           => 1,
         }
     );
-    $result = '        d        u  y0frey50      ba' unless $result;
+    $result = "        d        u  y0".$defaultlanguage."y50      ba" unless $result;
     my $f1 = substr( $result, 0, 8 );
     if ( $f1 eq '        ' ) {
         my @today = Date::Calc::Today();
diff --git a/installer/data/mysql/sysprefs.sql b/installer/data/mysql/sysprefs.sql
index fed22b64b3..387f977d6e 100644
--- a/installer/data/mysql/sysprefs.sql
+++ b/installer/data/mysql/sysprefs.sql
@@ -414,3 +414,4 @@ INSERT IGNORE INTO systempreferences (variable,value,explanation,options,type) V
 INSERT IGNORE INTO systempreferences (variable,value,explanation,options,type) VALUES('IDreamBooksResults','0','Display IDreamBooks.com rating in search results','','YesNo');
 INSERT INTO systempreferences (variable,value,options,explanation,type) VALUES ('OPACNumbersPreferPhrase','0', NULL, 'Control the use of phr operator in callnumber and standard number OPAC searches', 'YesNo');
 INSERT INTO systempreferences (variable,value,options,explanation,type) VALUES ('IntranetNumbersPreferPhrase','0', NULL, 'Control the use of phr operator in callnumber and standard number staff client searches', 'YesNo');
+INSERT INTO systempreferences (variable,value,explanation,options,type) VALUES('UNIMARCField100Language', 'fre','UNIMARC field 100 default language',NULL,'short');
diff --git a/installer/data/mysql/updatedatabase.pl b/installer/data/mysql/updatedatabase.pl
index 447b3fef4a..d4059cbfa7 100755
--- a/installer/data/mysql/updatedatabase.pl
+++ b/installer/data/mysql/updatedatabase.pl
@@ -6414,6 +6414,12 @@ if (C4::Context->preference("Version") < TransformToNum($DBversion)) {
     SetVersion ($DBversion);
 }
 
+$DBversion = "3.11.00.020";
+if ( C4::Context->preference("Version") < TransformToNum($DBversion) ) {
+    $dbh->do("INSERT INTO systempreferences (variable,value,explanation,options,type) VALUES('UNIMARCField100Language', 'fre','UNIMARC field 100 default language',NULL,'short')");
+    print "Upgrade to $DBversion done (Bug 8347 - Koha forces UNIMARC 100 field code language to 'fre')\n";
+    SetVersion($DBversion);
+}
 
 =head1 FUNCTIONS
 
diff --git a/koha-tmpl/intranet-tmpl/prog/en/modules/admin/preferences/cataloguing.pref b/koha-tmpl/intranet-tmpl/prog/en/modules/admin/preferences/cataloguing.pref
index c3a3847997..96f3603366 100644
--- a/koha-tmpl/intranet-tmpl/prog/en/modules/admin/preferences/cataloguing.pref
+++ b/koha-tmpl/intranet-tmpl/prog/en/modules/admin/preferences/cataloguing.pref
@@ -104,7 +104,11 @@ Cataloging:
         -
             - Define a list of subfields to use when prefilling items (separated by space)
             - pref: SubfieldsToUseWhenPrefill
-
+        -
+            - Use the languague (ISO 690-2)
+            - pref: UNIMARCField100Language
+              class: short
+            - as default language in the UNIMARC field 100 when creating a new record or in the field plugin.
     Display:
         -
             - 'Separate multiple displayed authors, series or subjects with '
diff --git a/kohaversion.pl b/kohaversion.pl
index ee3788d336..34495bd6dd 100644
--- a/kohaversion.pl
+++ b/kohaversion.pl
@@ -16,7 +16,7 @@ the kohaversion is divided in 4 parts :
 use strict;
 
 sub kohaversion {
-    our $VERSION = '3.11.00.019';
+    our $VERSION = '3.11.00.020';
     # version needs to be set this way
     # so that it can be picked up by Makefile.PL
     # during install