diff --git a/scripts/invoices/email_unpaid_invoices_to_customers.php b/scripts/invoices/email_unpaid_invoices_to_customers.php
index 81bf16a24cf..55a69f8cf76 100755
--- a/scripts/invoices/email_unpaid_invoices_to_customers.php
+++ b/scripts/invoices/email_unpaid_invoices_to_customers.php
@@ -177,7 +177,7 @@ function envoi_mail($mode,$oldemail,$message,$total,$userlang,$oldcustomer)
     global $conf,$langs;
 
     $newlangs=new Translate('',$conf);
-    $newlangs->setDefaultLang($userlang);
+    $newlangs->setDefaultLang(empty($userlang)?(empty($conf->global->MAIN_LANG_DEFAULT)?'auto':$conf->global->MAIN_LANG_DEFAULT):$userlang);
     $newlangs->load("main");
     $newlangs->load("bills");
 
diff --git a/scripts/invoices/email_unpaid_invoices_to_representatives.php b/scripts/invoices/email_unpaid_invoices_to_representatives.php
index 01837c47761..5774834e974 100755
--- a/scripts/invoices/email_unpaid_invoices_to_representatives.php
+++ b/scripts/invoices/email_unpaid_invoices_to_representatives.php
@@ -180,7 +180,7 @@ function envoi_mail($mode,$oldemail,$message,$total,$userlang,$oldsalerepresenta
     global $conf,$langs;
 
     $newlangs=new Translate('',$conf);
-    $newlangs->setDefaultLang($userlang);
+    $newlangs->setDefaultLang(empty($userlang)?(empty($conf->global->MAIN_LANG_DEFAULT)?'auto':$conf->global->MAIN_LANG_DEFAULT):$userlang);
     $newlangs->load("main");
     $newlangs->load("bills");