If someone is struggling to make firewing1 solution work, try this alternative:
1. Open sites/default/settings.php
2. Paste following code
<?php
$conf['i18nsync_fields_node'] = array(
'model' => 'SKU',
'list_price' => 'List Price',
'cost' => 'Cost',
'sell_price' => 'Sell Price',
'weight' => 'Weight',
'weight_units' => 'Weight Units',
'length' => 'Length',
'width' => 'Width',
'height' => 'Height',
'length_units' => 'Length Units',
'pkg_qty' => 'Quantity',
'default_qty' => 'Default quantity to add to cart'
);
?>Now you can enable syncing of these fields.