I18nTrait.php

<?php

namespace App;

use Carbon\Carbon;
use Illuminate\Support\Facades\Session as SessionFacade;

/**
 * Trait I18nTrait
 *
 * @package App
 */
trait I18nTrait
{
    /**
     * @var array
     */
    protected $translations = [];

    /**
     * @var string
     */
    protected $locale;

    /**
     * @param string $locale
     */
    public function setUserLocale(string $locale = 'de')
    {
        if (!in_array($locale, config('app.supported_locales'))) {
            throw new \InvalidArgumentException(trans('Provided locale is not supported'));
        }
        
        $this->locale = $locale;

        app()->setLocale($locale);
        SessionFacade::put('_locale', $locale);
        Carbon::setLocale($locale);
    }

    /**
     * @param string $key
     *
     * @return string
     */
    public function translate(string $key): string
    {
        if (!isset($this->translations[$this->locale])) {
            $this->translations[$this->locale] = include(resource_path(sprintf('lang/%s/messages.php', $this->locale)));
        }

        if (isset($this->translations[$this->locale][$key])) {
            return $this->translations[$this->locale][$key];
        }

        // Default, return key again as no translation was found for current locale...
        return $key;
    }
}