It is a line in the file login.php in v.3.2.3 (nr. 135):
echo '<p class="center"><strong>' . WT_I18N::translate('Welcome to this genealogy website') . '</strong>';
In next release that line is removed as it should not have been there. The same text is repeated in the block of welcome text below.
You have that line in the code
You do not have it in your Danish translation file, because your .po file is later than the one released with 3.2.3 and already has that line of translation removed, so in Danish it is not translated any more.
Easy solution – remove that line from login.php. Perhaps modify your translation of the text below it if you want to include those words.