drush option --language to extract translations

I do not know if I am missing something...
In an older (quite old) 8.x-1.x dev version there was a drush option "--language" to not only collect the strings to be translated but to also include existing translations.

I did not found anything in the issues according this (or a similiar) option.

Comparing my old version to current dev I found some small differences in potx.drush.inc.

I do not really understand the internals but I just added the option "--language" and changed the call to _potx_build_files():

@@ -22,6 +22,7 @@ function potx_drush_command() {
       'files' => 'Comma delimited list of files to extract translatable strings from.',
       'folder' => 'Folder to begin translation extraction in. When no other option is set this defaults to current directory.',
       'api' => 'Drupal core version to use for extraction settings.',
+      'language' => 'language to include in the po file',
     ],
     'examples' => [
       'potx single' => 'Extract translatable strings from applicable files in current directory and write to single output file',
@@ -75,6 +76,7 @@ function potx_drush_extract($mode = NULL) {
   $files_option = drush_get_option('files');
   $folder_option = drush_get_option('folder');
   $api_option = drush_get_option('api');
+  $language_option = drush_get_option('language');
   if (empty($api_option) || !in_array($api_option, [5, 6, 7, 8])) {
     $api_option = POTX_API_CURRENT;
   }
@@ -105,7 +107,16 @@ function potx_drush_extract($mode = NULL) {
 
   potx_finish_processing('_potx_save_string', $api_option);
 
-  _potx_build_files(POTX_STRING_RUNTIME, $build_mode);
+  _potx_build_files(
+    POTX_STRING_RUNTIME,
+    $build_mode,
+    'general',
+    '_potx_save_string',
+    '_potx_save_version',
+    '_potx_get_header',
+    $language_option,
+    $language_option
+   );
   _potx_build_files(POTX_STRING_INSTALLER, POTX_BUILD_SINGLE, 'installer');
   _potx_write_files();

Worked like a charm :)