I Finally fixed it myself. add the next lines to your web.config system.webserver section (for each multi language country/culture). The examples are for swiss only, but ofcourse you need to do this for belgium as well:

If you are running on Azure / the episerver digital cloud expierence platform also add:

<system.webServer>
    <urlCompression doStaticCompression="true" doDynamicCompression="false" dynamicCompressionBeforeCache="true" />

<rewrite>
      <rules>
        
        <!--swiss language redirects-->
        <rule name="de-ch" patternSyntax="ECMAScript" stopProcessing="true">
          <match url="de-ch.*" ignoreCase="true" />
          <conditions logicalGrouping="MatchAll" trackAllCaptures="true">
            <add input="{HTTP_HOST}" pattern="(.*).domainname.(?!ch)" ignoreCase="true" />
            <add input="{REQUEST_URI}" pattern="episerver/cms" ignoreCase="true" negate="true" />
          </conditions>
          <action type="Redirect" url="http://{C:1}.domainname.ch/{R:0}" />
        </rule>

        <rule name="fr-ch" patternSyntax="ECMAScript" stopProcessing="true">
          <match url="fr-ch.*" ignoreCase="true" />
          <conditions logicalGrouping="MatchAll" trackAllCaptures="true">
            <add input="{HTTP_HOST}" pattern="(.*).domainname.(?!ch)" ignoreCase="true" />
            <add input="{REQUEST_URI}" pattern="episerver/cms" ignoreCase="true" negate="true" />
          </conditions>
          <action type="Redirect" url="http://{C:1}.domainname.ch/{R:0}" />
        </rule>
      
      </rules>
      <outboundRules>

        <preConditions>
          <preCondition name="IsHTML">
            <add input="{RESPONSE_CONTENT_TYPE}" pattern="^text/html" />
          </preCondition>
        </preConditions>

        <!--swiss outbound redirects-->
        <rule name="fr-ch" patternSyntax="ECMAScript" preCondition="IsHTML">
          <match filterByTags="A" pattern="fr-ch.*" ignoreCase="true" />
          <conditions logicalGrouping="MatchAll" trackAllCaptures="true">
            <add input="{HTTP_HOST}" pattern="(.*).domainname.(?!ch)" />
            <add input="{REQUEST_URI}" pattern="episerver/cms" negate="true" />
          </conditions>
          <action type="Rewrite" value="http://{C:1}.domainname.ch/{R:0}" />
        </rule>

        <rule name="de-ch" patternSyntax="ECMAScript" preCondition="IsHTML">
          <match filterByTags="A" pattern="de-ch.*" ignoreCase="true" />
          <conditions logicalGrouping="MatchAll" trackAllCaptures="true">
            <add input="{HTTP_HOST}" pattern="(.*).domainname.(?!ch)" />
            <add input="{REQUEST_URI}" pattern="episerver/cms" negate="true" />
          </conditions>
          <action type="Rewrite" value="http://{C:1}.domainname.ch/{R:0}" />
        </rule>

      </outboundRules>
    </rewrite>