Elgg has several shortcomings when it comes to support for multiple languages. I have mentioned this in a topic here :

http://community.elgg.org/mod/groups/topicposts.php?topic=569316&group_guid=211069

And a ticket is sent to trac about categories: http://trac.elgg.org/ticket/2381

So...not possible yet, due to shortcomings in the current elgg core?

But isn't this a show-stopper? Are there no international elgg sites? or how do they solve these issues?

On my site I have made a new theme from scratch that include custom external pages on which I show the content using language variables.

Elggzone_darkgrey happens to be the first and only theme I tried so far. I like it. As far as I can see I might just need to change the topbar, some css, and...

But I cannot find language dependant code in this theme. Is it in some other theme? Could you not make it into a separate plugin or give some code hints, so I could use it in any theme/plugin?

A few language variables are added in mod/elggzone_darkgrey/languages/en.php

The theme darkgrey is made for this community and does not include custom external pages only elgg default external pages.

By my site I meant this site http://www.me4real.com and that's another theme.

So in your theme you override externalpages views so they do not use elgg_get_entities() or  ElggObject.save(), but use elgg_echo("custom_field") instead? Or did you somehow tweak it to store in / filter out different languages in /out the database? 

Yes, <?php echo elgg_echo('var'); ?>