Problem dynamically populating a select field based on the selection of another select field
You're wrapping your model select options array in t()

i.e: '#options' =&gt; t($models) vs '#options' =&gt; $models

Try this instead, it might work:

  $form['model'] = array(
    '#type' =&gt; 'select',
    '#options' =&gt; $models,
    '#prefix' =&gt; '&lt;div id="model_div"&gt;',
    '#suffix' =&gt; '&lt;/div&gt;',
  );