The page you gave me above shows how to produce multiple installers per language. That brought me to the idea to handle that automatically in CPack. 
Something like this:

const char* const cultures = GetOption("CPACK_WIX_CULTURES");
if(strstr(cultures, ";"))
{
    // we have a list of cultures -> generate multiple installers
}
else
{
    // generate a single installer
}

What do you think about that?