The simplest way to tell the preferred language on your site is to set language based on host.
You go to Admin Mode -> Config Tab -> Manage Websites -> Select your website to edit.
Either create your host name or add your host "mysite.dk".
Select which Culture you want to display.
If you have created a content in wrong language branch and you need change master language for all content there is a Sql script for this (not sure if this is officially supported). Some roots are here (login required) - https://www.coderesort.com/svn/epicode/EPiCode.LanguageTool/EPiCode.LanguageTools/ChangePageBranchMasterLanguage.sql
For 7.5 you can contact EPi Support to get a copy of the script. It helped a lot when in the middle of half translated content we realized that we were working on wrong language branch ;)
I have multi-language site where I need the default language to be danish. That is, when the user goes to mysite.dk the start page displayed should be the one from the danish language branch. However, per default EPiServer displays the english version of the page. Using mysite.dk/da or mysite.dk/en I get the expected start page version displayed.
I've tried making a fresh install of the EPiServer db using the steps in https://hanskindberg.wordpress.com/2014/02/18/episerver-cms-7-5-svenska-as-master-language/, which did change the rootpage to danish, but when I create a start page in both a danish and english version, it is still the english one being displayed.
So, how do I change the default master language of my site?
Any help will be much appreciated.