how can change foreach array to getting a item in php 7.4 (I didn’t have problem in php 5.4) [duplicate]

I didn’t have problem with this function in php 5.4 but in upgrading script i have this probem. my function in the function.php file through which I call the language files of the project.

class sblib {
    var $sblang = "";
    var $lang = "";

    function load_lang($file_lang) {
        global $sbportals;
        $mlang = $this->sblang;
        if ($sbportals->member['sb_lang']) {    
            $dir = @opendir($this->sitepath."sbportal/lang/");
            while (($dirt = readdir($dir)) !== false) {
                $sbl = strtolower (substr($dirt, 0, 3));        
                $bol = strtolower (substr($sbportals->member['sb_lang'], 0, 3));
                if ($sbl == $bol && $dirt != ".htaccess" && $dirt != "htaccess" && $dirt != "index.html" && $dirt != "English_Reference") {
                    $mlang = $this->sitepath."sbportal/lang/".$dirt;
                }   
            }   
            closedir($dir);
        }

        require "$mlang/$file_lang";
        foreach ($langsb as $k => $v) {

            $this->lang[$k] = stripslashes($v);////this line///

            }
    }

    $sblib = new sblib;
    $sblib->stimer();
    $sblib->sblang = $sb_PATH."sbportal/lang/".$sb_LANG;

This is the content of the language file (lang_search.php):

$langsb['ad_langs_group'] = "Group";
$langsb['ad_langs_group_title'] = "Group Title";
$langsb['ad_langs_sel_title'] = "Language Administration";
$langsb['ad_langs_sel_info'] = "Choose the language";

Then by calling the function (once in each file of the project) as follows

$sblib->load_lang("lang_search.php");

And using the calling function wherever I need as below

{$sblib->lang['download']}

I can use translation files for translate of each words. I had no problem until php 5.6, but I see this error when upgrading to 7.4.

Warning: Illegal.string.offset.'download'.in ... (////this line///)

please help me to solve.

I have checked all the ways and pages of the stackoverflow.