Unsupported operand types in lang_dropdown.module on line 232

I can't see anything wrong in line 232. There is an union of arrays in that line and the operands are arrays so I don't see why you receive an unsupported operand types error.

Line 32

$form += $hidden_elements;

The only thing I can imagine is that $hidden_elements is NULL. But that shouldn't happen ever.

So I only can suggest to debug to try to understand why that's happening. You can just add before that line 232:

debug($languages);
debug($form);
debug($hidden_elements);

And with all that output probably we can try to guess what's happening.

I don't understand how you have created that node in a way that all languages claims there is no translation.

      array (
        'class' => 'locale-untranslated',
      ),

so no of them has a href property. I can make a check to just don't show the language switcher at all in that case to avoid that weird problem. Adding this just before line 232:

if ($hidden_elements === NULL) return array();

should resolve that. But you should look why that is happening. What happens on that node if you enable the Drupal core language switcher block?
It seems as if you had created a node with no language but it is not a language neutral node either and I can't understand how you have done that. When you create a node in its language select you can choose one language or the "language neutral" option. There isn't any "no language" option.
The only thing I can imagine is if maybe the node is created with a language and later that language is removed from the list of available languages. Maybe in that case the node falls in that 'no language' state.

Ok I think that is the problem, a node in a language that later is disabled or deleted.

The solution is to don't show language switcher at all in that case. Changing line 232:

$form += $hidden_elements;

to:

if (!isset($hidden_elements)) return array();
$form += $hidden_elements;

As a protection to avoid this weird problem that can happen in this case.

But the real solution is reenable the language in which that node is writen if you pretend to use that language.

Could you edit node just to save it and then debug again the $languages variable to show here its content?

In that variable Spanish should have a href with the node url and language-link as a class in attributes:

    'es' => 
    array (
      'href' => '.../...',
...
...
...
     'attributes' => 
      array (
        'class' => 
        array (
          0 => 'language-link',
        ),
      ),
...
...
...

I don't know whats wrong with that node that in my opinion has incorrect values in $languages variable.

Can you show your $languages variable in different node? Same debug in language dropdown switcher but in a node in which language switcher works fine.

I'm going to include the check code in language dropdown switcher to avoid this situation but the problem with your node is not related to language dropdown switcher and is really strange.

I'm going to push the following patch to solve this.

Is this patch committed? If not, it should be RTBC.

If it helps to clarify what may have been happening, here is how I produced the error:

1. Create a site and enable three languages (English, Spanish, French).
2. Create some nodes, and provide translations in all three languages.
3. Later, disable one of the languages (e.g. German).
4. Try to create a new node, then recieve this error.

The patch seems to fix everything, so +1 on getting this committed.

Still a bug but patch fixes everything

Just had a look at the dev it looks like the patch is committed there. No idea when...