Load correct language Ajax
One issue may be that your javascript is requesting a specific url as defined from the site root, thus not giving craft the opportunity to do it's locale routing magic (keep in mind the url for languages other than the default locale may actually be '/no/loadmore.html' — or however you have defined the locale routes in your config settings). So just changing the request url in javascript may solve the problem.

$('.third_article_module').load('loadmore');


Another thing to keep in mind in general is that you can always specify a locale as part of the query, if you ever need to bypass or override craft's locale routing for some reason.

{% set locale = craft.i18n.getCurrentLocale() %}
{% set entries = craft.entries.section('artikkel').locale(locale).order('dateCreated desc') %}
{% for entry in entries %}
    ...
{% endfor %}


Another thing worth mentioning is that you could potentially also ajax load content from the current page template by using an isAjax conditional, thus eliminating the need for a separate 'loadmore' template altogether.

{% if not craft.request.isAjax %}
    {# render page content #}
{% endif %}

{% if craft.request.isAjax %}
    {# render loadmore content #}
{% endif %}


You can then just pass the entry url to your javascript and ajax load the current page (in this case I'm passing the url by defining a 'data-url' attribute on the .showmemore_inner h2 dom element; i.e. &lt;h2 data-url="{{ entry.url }}"&gt;).

$('.showmemore_inner h2').on("click", function(e){
    e.preventDefault();
    var url = $(this).attr('data-url');
    $('.third_article_module').load(url);
    $('h2.lasterinn').css('display', 'block');
});


Note: also e.preventDefault() should come before any return statement or else it will never get a chance to fire.