--- includes/locale.inc	2009-08-22 15:34:17.000000000 +0100
+++ includes/locale.inc	2009-09-05 17:56:54.000000000 +0100
@@ -1208,7 +1208,7 @@ function _locale_import_po($file, $langc
 }
 
 /**
- * Parses Gettext Portable Object file into an array
+ * Open and passes on Gettext Portable Object file for parsing
  *
  * @param $op
  *   Storage operation type: db-store or mem-store
@@ -1223,18 +1223,66 @@ function _locale_import_po($file, $langc
  */
 function _locale_import_read_po($op, $file, $mode = NULL, $lang = NULL, $group = 'default') {
 
-  $fd = fopen($file->uri, "rb"); // File will get closed by PHP on return
-  if (!$fd) {
-    _locale_import_message('The translation import failed, because the file %filename could not be read.', $file);
+  if ($size = filesize($file->uri)) {
+    // File will get closed by PHP on return.
+    $fd = fopen(drupal_realpath($file->uri), "rb");
+    if (!$fd) {
+      _locale_import_message('The translation import failed, because the file %filename could not be read.', $file);
+      return FALSE;
+    }
+
+    // If the file size is above our seek limit, we try and seek into the file
+    // in small chunks.
+    if ($size > variable_get('locale_import_po_seek_limit', 50000)) {
+      $chunk_size = variable_get('locale_import_po_chunk_size', 100);
+      $seek_position = 0;
+      while(is_int($seek_position = _locale_import_parse_po($op, $file, $fd, $mode, $lang, $group, $seek_position, $chunk_size)));
+    }
+    else {
+      _locale_import_parse_po($op, $file, $fd, $mode, $lang, $group);
+    }
+  }
+  else {
+    _locale_import_message('The translation import failed, because the file %filename could not be found or was empty.', $file);
     return FALSE;
   }
+  
+}
+
+/**
+ * Parses Gettext Portable Object file into an array
+ *
+ * @param $op
+ *   Storage operation type: db-store or mem-store
+ * @param $file
+ *   Drupal file object corresponding to the PO file being imported
+ * @param $fd
+ *   File system pointer for the same PO file, opened by _locale_import_read_po
+ * @param $mode
+ *   Should existing translations be replaced LOCALE_IMPORT_KEEP or LOCALE_IMPORT_OVERWRITE
+ * @param $lang
+ *   Language code
+ * @param $group
+ *   Text group to import PO file into (eg. 'default' for interface translations)
+ * @param $seek_position
+ *   Position from which to start/continue parsing (that position returned by this function in a previous
+ *   iteration)
+ * @param $chunk_size
+ *   Approximate number of lines to parse in one iteration - but continue to end of current entry.  If not
+ *   set, or set to zero, continue to end of file.
+ */
+function _locale_import_parse_po($op, $file, $fd, $mode = NULL, $lang = NULL, $group = 'default', $seek_position = NULL, $chunk_size = NULL) {
 
   $context = "COMMENT"; // Parser context: COMMENT, MSGID, MSGID_PLURAL, MSGSTR and MSGSTR_ARR
   $current = array();   // Current entry being read
   $plural = 0;          // Current plural form
   $lineno = 0;          // Current line
-
+  // Set file position indicator to where previous iteration left off.
+  if ($seek_position !== NULL) {
+    fseek($fd, $seek_position);
+  }
   while (!feof($fd)) {
+    $seek_position_before_line = ftell($fd);
     $line = fgets($fd, 10*1024); // A line should not be this long
     if ($lineno == 0) {
       // The first line might come with a UTF-8 BOM, which should be removed.
@@ -1247,11 +1295,17 @@ function _locale_import_read_po($op, $fi
       if ($context == "COMMENT") { // Already in comment context: add
         $current["#"][] = substr($line, 1);
       }
-      elseif (($context == "MSGSTR") || ($context == "MSGSTR_ARR")) { // End current entry, start a new one
+      elseif (($context == "MSGSTR") || ($context == "MSGSTR_ARR")) {
+        // End current entry, start a new one, or end iteration if chunk too long.
         _locale_import_one_string($op, $current, $mode, $lang, $file, $group);
         $current = array();
-        $current["#"][] = substr($line, 1);
-        $context = "COMMENT";
+        if ($chunk_size && ($lineno > $chunk_size)) {
+          return ($seek_position_before_line);
+        }
+        else {
+          $current["#"][] = substr($line, 1);
+          $context = "COMMENT";
+        }
       }
       else { // Parse error
         _locale_import_message('The translation file %filename contains an error: "msgstr" was expected but not found on line %line.', $file, $lineno);
@@ -1273,9 +1327,12 @@ function _locale_import_read_po($op, $fi
       $context = "MSGID_PLURAL";
     }
     elseif (!strncmp("msgid", $line, 5)) {
-      if ($context == "MSGSTR") {   // End current entry, start a new one
+      if ($context == "MSGSTR") {   // End current entry, start a new one, or end iteration if chunk too long
         _locale_import_one_string($op, $current, $mode, $lang, $file, $group);
         $current = array();
+        if ($chunk_size && ($lineno > $chunk_size)) {
+          return ($seek_position_before_line);
+        }
       }
       elseif ($context == "MSGID") { // Already in this context? Parse error
         _locale_import_message('The translation file %filename contains an error: "msgid" is unexpected on line %line.', $file, $lineno);
@@ -1370,12 +1427,12 @@ function _locale_import_read_po($op, $fi
   // End of PO file, flush last entry
   if (!empty($current) && !empty($current['msgstr'])) {
     _locale_import_one_string($op, $current, $mode, $lang, $file, $group);
+    return TRUE;
   }
   elseif ($context != "COMMENT") {
     _locale_import_message('The translation file %filename ended unexpectedly at line %line.', $file, $lineno);
     return FALSE;
   }
-
 }
 
 /**