T3BLOG

DIRECTORY_SEPARATOR uses seperator from system.
Under Windows this is a backslash under Linux a slash (I like slash ;) )
Typo will make even the same seperator in Linux as in Windows.

The Problem is under Windows:
Path_From_Typo . DIRECTORY_SEPARATOR . "tabulator" = C:/virtual/typo3/typo3conf/ext\tabulator

PHP will interpret the \t as an tabulator (\n, \e) and this will result in an unknown path

It does not work like that. If you write $str = '\t', it is a tab character. If you write $c = '\\'; $str = $c . 't', it is not a tab character but a slash followed by a 't' character. It is PHP basics.

The real problem seems to in t3lib_div::getFileAbsFileName(), which hard-codes a forward slash as a separator. Thus language file with valid Windows path separator cannot be read. If your idea was right, you would not even see "? - ?" because the directory with widgets would not be found:

        $dir = opendir($searchInFolder);
        while (($file = readdir($dir)) !== false) {
            if ($file{0} != '.') {
                $testPath = $searchInFolder . DIRECTORY_SEPARATOR . $file;
                if (is_dir($testPath) && file_exists($testPath . DIRECTORY_SEPARATOR . 'locallang.xml')) {
                    $files[$file] = $testPath;
                }
            }
        }
        closedir($dir);