URL Structure Problem

I resolved it with

putting the following as index.php in the template for ‘/’

?php
/**
 * The main template file.
 *
 * This is the most generic template file in a WordPress theme
 * and one of the two required files for a theme (the other being style.css).
 * It is used to display a page when nothing more specific matches a query.
 * E.g., it puts together the home page when no home.php file exists.
 * Learn more: http://codex.wordpress.org/Template_Hierarchy
 *
 * @package WordPress
 * @subpackage Redirect
 */

/**
 * Detect browser language.
 *
 * @param array $allowed_languages An array of languages that are available on the site.
 * @param string $default_language Default language to use if none could be detected.
 * @param string $lang_variable Custom user language support. If not specified $_SERVER['HTTP_ACCEPT_LANGUAGE'] is used.
 * @param string $strict_mode If true (default) the whole language code ("en-us") is used and not only the left part ("en").
 * @return string The detected browser language.
 */
function get_lang_from_browser($allowed_languages, $default_language, $lang_variable = NULL, $strict_mode = TRUE) {
    // Use $_SERVER['HTTP_ACCEPT_LANGUAGE'] if no language variable is available
    if (NULL === $lang_variable)
        $lang_variable = $_SERVER['HTTP_ACCEPT_LANGUAGE'];

    // Any info sent?
    if (empty($lang_variable))
        return $default_language;

    // Split the header
    $accepted_languages = preg_split('/,\s*/', $lang_variable);

    // Set default values
    $current_lang = $default_language;
    $current_q    = 0;
    // Now work through all included languages
    foreach ($accepted_languages as $accepted_language) {
        // Get all info about this language
        $res = preg_match(
            '/^([a-z]{1,8}(?:-[a-z]{1,8})*)'.
            '(?:;\s*q=(0(?:\.[0-9]{1,3})?|1(?:\.0{1,3})?))?$/i',
            $accepted_language,
            $matches
        );

        if (!$res)
            continue;

        // Get language code and split into parts immediately
        $lang_code = explode('-', $matches[1]);

        // Is there a quality set?
        if (isset($matches[2]))
            $lang_quality = (float)$matches[2];
        else
            $lang_quality = 1.0;

        // Until the language code is empty...
        while (count($lang_code)) {
            // Check if the language code is available
            if (in_array(strtolower(join('-', $lang_code)), $allowed_languages)) {
                // Check quality
                if ($lang_quality > $current_q) {
                    $current_lang = strtolower(join('-', $lang_code));
                    $current_q = $lang_quality;
                    break;
                }
            }
            // If we're in strict mode we won't try to minimalize the language
            if ($strict_mode)
                break;

            // Cut the most right part of the language code
            array_pop($lang_code);
        }
    }

    return $current_lang;
}

$allowed_langs = array('en', 'de', 'es');
$lang = get_lang_from_browser($allowed_langs, 'en', NULL, FALSE);
header('Location: http://' . $_SERVER['HTTP_HOST'] . "/$lang/");

exit();
?>

If you generate it as blank theme you should also put some styles.css in that Theme folder.

Works great, seams to be German engineering your plugin 🙂