I'd like to offer save users language_code and publish class with main logic for fast start #721

$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,
         //...
]

$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;
    }

}