$table->string('language_code')->nullable();

protected function setupChat(){
//your code...
if (!$this->chat->exists) {
 if (!$this->allowUnknownChat()) {
 throw new NotFoundHttpException();
 }
 if (config('telegraph.security.store_unknown_chats_in_db', false)) {
 $this->createChat($telegramChat, $this->chat);
 //mine part:
 //save original lang and if it is not supported by you, will save the suppored lang code to DB
 $tgData = $this->message->toArray();
 $lang = lng_def();
 if(isset($tgData['from']['language_code']) and ctype_alpha($tgData['from']['language_code'])){
 $lang = $tgData['from']['language_code'];
 TelegraphChat::where([
 'id' => $this->chat['id'],
 'chat_id' => $this->chat['chat_id'],
 'telegraph_bot_id' => $this->chat['telegraph_bot_id'],
 ])->update(['language_code' => $lang]);
 }
 $this->chat->language_code = $this->TC_set_supported_lang($lang);
 //end of mine part
 }
 }
}

if (!function_exists('lng_def')) { function lng_def(){return /**set your**/ 'ru';}}
if (!function_exists('lng_falbk')) { function lng_falbk(){return 'en';/**because Laravel default is English**/}}
if (!function_exists('lng_sup_arr')) { function lng_sup_arr(){return ['ru'];}}
if (!function_exists('t')) { function t($w,$assocParams=[],$hardLocale=null){return __('t.'.$w,$assocParams,$hardLocale);}}

'webhook' => [
 //your code....
 'handler' => App\Http\Telegas\TeleGraphAndGram::class,
 //...
]

php artisan vendor:publish --tag=telegraph-add-default-controller-to-http-folder

$this->publishes([
 __DIR__ . '/Http/TeleGraphAndGram.php' => app_path('Http/TeleGraphAndGram.php'),
], 'telegraph-add-default-controller-to-http-folder');

<?php
namespace App\Http;
use DefStudio\Telegraph\Facades\Telegraph;
use DefStudio\Telegraph\Handlers\WebhookHandler;
use Illuminate\Support\Stringable;
class TeleGraphAndGram extends WebhookHandler
{
 protected $lang_of_user_supported = true;
 protected $lang_of_user_orig = '';
 public function __construct()
 {
 parent::__construct();
 app()->setLocale(lng_def());//hardcode, but only when you have 1 language and it is no English and you want start fast
 }
 public function handleUnknownCommand(Stringable $text): void
 {
 $this->reply('<b>No such command</b>');
 // some help to juniors:
 // or Telegraph::message('...')->send();
 // or $this->chat->html('Your text is: <i>'.$text.'</i>')->send();
 }
 public function start(): void
 {
 $lang_of_user_supported = $this->lang_of_user_supported ? '' : t('lang_not_supported',['LANG'=>$this->lang_of_user_orig], lng_falbk());
 if($lang_of_user_supported){
 $this->chat->html($lang_of_user_supported)->send();
 }
 $this->reply('Time to start');
 }
 public function handleChatMessage(Stringable $text): void
 {
 $this->chat->html('Your text is: <i>'.$text.'</i>')->send();
 /**
 * To receive a photo (not a document!!)
 */
 //$photo = $this->message->photos()->toArray();
 //$data = count($photo)-1;
 //$id_photo = $photo[$data]['id'];
 //$this->bot->store($id_photo, $this->folder_for_photo(), Str::random(11).'.jpg');
 }
 public function TC_set_supported_lang($lang_from_user){
 // if lang is not supported , set 1st supported and answer with fallback
 // and continue with RU
 $lang_from_user = mb_strtolower($lang_from_user);
 $this->lang_of_user_orig = $lang_from_user;
 if(!in_array($lang_from_user, lng_sup_arr())){
 $set_lang = lng_def();
 $this->chat->language_code = $set_lang;
 TelegraphChat::where([
 'id' => $this->chat['id'],
 'chat_id' => $this->chat['chat_id'],
 'telegraph_bot_id' => $this->chat['telegraph_bot_id'],
 ])->update(['language_code' => $set_lang]);
 $this->lang_of_user_supported = false;
 }else{$set_lang = $lang_from_user;}
 
 return $set_lang;
 }
}