Incompatible with localized/translated content

I've tried Unique Field 7.x-1.0-beta1, in a Drupal 7 installation, with default language set to Spanish.

On editing nodes, the following messages are registered on watchdog, and Unique Field won't detected repeated values:

Warning: Invalid argument supplied for foreach() en unique_field_node_validate() (línea 168 de /var/www/drupal/sites/default/modules/unique_field/unique_field.module).

Warning: array_values() expects parameter 1 to be array, null given en _field_filter_items() (línea 494 de /var/www/drupal/modules/field/field.module).

The problem seems to be in these lines:

166          $f = $node->$field;
167          $values = $f[LANGUAGE_NONE];
168          foreach ($values as $index => $value) {
                [..]
             }

In my installation, the $f variable is indexed with the 'es' language code:

array(1) {
  ["es"]=> array(1) { [0]=> array(1) { ["email"]=> string(22) "yyyyyy@gmail.com" } } 
}

So, the $f[LANGUAGE_NONE] (aka $f['und']) element is undefined, the field content is in $f['es'] instead.

See Field Language API

Thank you in advance, for your help.