How to dynamically make a field visible?
You miss ] in the selector ':input[name="field_type[und]"' code test with the following it will work.

':input[name="field_type[und]"]' =&gt; ['value' =&gt; 'interne'],


Update:
The state work with any valid JQuery selector, so if you looking to target it with select selector instead of :input you can use this:

 'select[name="field_type[und]"]' =&gt; ['value' =&gt; 'interne'],