<p>I'm looking for a way to set the default language for visitors comming to a site built in EPiServer for the first time. Not just administrators/editors in the backend, people comming to the public site.</p>

Depends on your setup.
If the site languages is to change under different domains you can do this.
Add to configuration -> configSections nodes in web.config:
```
```
<sectionGroup name="episerver">
  <section name="domainLanguageMappings" allowDefinition="MachineToApplication" allowLocation="false" type="EPiServer.Util.DomainLanguageConfigurationHandler,EPiServer" />
```
```
..and add this to episerver node in web.config:
```
```
<domainLanguageMappings>
    <map domain="site.com" language="EN" />
    <map domain="site.se" language="SV" />
  </domainLanguageMappings>
```
```
Otherwhise you can do something like this.
Add to appSettings in web.config:
```
```
<add name="EPsDefaultLanguageBranch" key="EN"/>
```
```