Generate XML Feed / RSS Feed with "nested" elements.

You cannot use a for loop in your array definition, try this

// create the array
$xml_elements = array(
  array(
    'key' => 'descriptionENG',
    'value' => $node->field_description_english[0]['safe'],
  ),
  array(
    'key' => 'descriptionDUT',
    'value' => $node->field_description_dutch[0]['safe'],
  ),
);
// then add the other items to your array
foreach ($node->field_related_projects as $relatedproject) {   
  //  when you add an item to an array with [] it adds the item with a 
  //  sequencial key, i.e. 0, 1, 2, 3,...
  $xml_elements['relatedProjects'][] = array(
    'key' => 'relatedProjects',
    'value' => $relatedproject,
  );
}

Some advice -
Figure out the legal ways of extending RSS before you get much more into customizing like that.
It is TOTALLY supported to add your own tags, but you should find out about namespaces and go from there.
Not only will it stop your current output from being totally invalid, like it is now, but you will also get the advantages of mash-ups.
http://developer.cooliris.com/ piclens sorta demonstrates how this can be achieved, and be really cool.
http://www.vast.com/rss/real_estate is another example of specific data embedded in valid feeds to extend them

If, at the moment, you are control of both the server and the consumer application, you can choose your syntax carefully.

Also, there are supported ways to embed translations in RSS, I think it's like

<description xml:lang="en"> ......... </description>
<description xml:lang="nl"> ......... </description>

Standards are cool ... when you can find ways to make them work FOR you.

This reading may help on the lang syntax on XML HTML RSS elements
... I can't speak for the actual support in RSS readers tho...

And here is some info about extending RSS (OK, actually ATOM, but the theory should apply)

Here is an RSS reference demonstrating a few other extensions

Not sure about the php code you need either, I don't use contemplate, but it should be possible, or made possible to add arbitrary attributes.

for adding attributes check out the documentation for format_xml_elements(), which is the function being used to translate the array to an XML string.

for example to get:

<relatedprojects>
    <relatedproject type="something">namegoeshere</relatedproject>
</relatedprojects>

do

$xml_element = array(
    'relatedprojects' => array(
        'key' => 'relatedproject',
        'value' => 'namegoeshere',
        'attributes' => array (
            'type' => 'something',
        )
    )
);

Really cool, thanks
Bizarrely, I have format_xml_elements() open in another window right now on a TOTALLY unrelated issue tracking down why it's giving PHP_STRICT warnings in an otherwise clean install :)
That's just freaky.

I'm interested in getting this to work but it doesn't work for me.
Using $xml_element in the Contemplate RSS Template blocks returns nothing.

I read this is a Drupal 6 issue, ???

I just want to add extra xml tags to my rss feed

@egeos,

notice: this is not an issue, this is a support request.

Yes you can add extra xml tags using contemplate. if you would like to add your own issue I would be glad to help you.

I am going to assume that this is fixed since there has been no more comments posted

subscribe

FYI, and for reference, here's the custom code I added to the contemplate RSS for an Ubercart product to start to support Google Merchant syndication:

<?php 
print($node->teaser) ; 

// Add google merchant-compatible namespaced tags
$xml_elements = array();

if (!empty($node->sell_price)) {
  $xml_elements[] = array(
    'key' => 'g:price',
    'value' => $node->sell_price,
    'namespace' => array('xmlns:g' => 'http://base.google.com/ns/1.0'),
  );
}
if (!empty($node->model)) {
  $xml_elements[] = array(
    'key' => 'g:id',
    'value' => $node->model,
    'namespace' => array('xmlns:g' => 'http://base.google.com/ns/1.0'),
  );
}
?>

PHP tags required.

I'm actually going to roll this and more into a custom module that supports ubercart, but this worked when I was in the testing phase.
(Took me a few hours of research to get this far, so I though I'd share)