einundzwanzig-portal/app/Http/Livewire/Frontend/Header.php

<?php

namespace App\Http\Livewire\Frontend;

use App\Models\City;
use App\Models\Country;
use Illuminate\Support\Facades\Route;
use Livewire\Component;

class Header extends Component
{
    public Country $country;
    public $currentRouteName;
    public string $c = 'de';

    public function rules()
    {
        return [
            'c' => 'required',
        ];
    }

    public function mount()
    {
        $this->currentRouteName = Route::currentRouteName();
        $this->c = $this->country->code;
    }

    public function updatedC($value)
    {
        return to_route($this->currentRouteName, ['country' => $value]);
    }

    public function render()
    {
        return view('livewire.frontend.header', [
            'cities' => City::query()
                            ->select(['latitude', 'longitude'])
                            ->get(),
        ]);
    }
}