Set the Laravel app locale from any URL within a group with a fallback to the default locale.

app.php

<?php

return [
  
    'supported_locales' => [
        'en',
        'fr',
        'de',
    ],
    
];

footer.blade.php

@foreach(supported_locales() as $locale)
    <li class="dib">
        <a href="{{ localized_url($locale) }}" title="Switch to the {{ mb_strtoupper($locale) }} version" class="db link dim mid-gray">{{ mb_strtoupper($locale) }}</a>
    </li>
@endforeach

helpers.php

if (! function_exists('localized_url')) {
    /**
     * @param string $locale
     * @param string|null $url
     *
     * @return string
     */
    function localized_url(string $locale, string $url = null) : string
    {
        return Localizer::getLocalizedUrl($locale, $url);
    }
}

Localizer.php

<?php

declare(strict_types=1);

namespace App\Managers;

use Illuminate\Http\Request;

class Localizer
{
    /**
     * @var \Illuminate\Http\Request
     */
    protected $request;

    /**
     * @param \Illuminate\Http\Request $request
     */
    public function __construct(Request $request)
    {
        $this->request = $request;
    }

    /**
     * Load the application in a given locale or fall back to the default if none given.
     *
     * @return string|null
     */
    public function setLocale() : ?string
    {
        $requestedLocale = $this->request->segment(1);

        if (in_array($requestedLocale, supported_locales())) {
            $locale = $requestedLocale;
        }
        else {
            $locale = locale();
            $requestedLocale = null;
        }

        app()->setLocale($locale);

        return $requestedLocale;
    }

    /**
     * @param string $locale
     * @param string|null $url
     *
     * @return string
     */
    public function getLocalizedUrl(string $locale, string $url = null) : string
    {
        $url = $url ?? current_url();

        // The URL path can be empty, so make sure a default is set
        ['scheme' => $scheme, 'host' => $host, 'path' => $path] = array_merge(['path' => null], parse_url($url));

        $path = ! is_null($path) ? explode('/', substr($path, 1)) : [];

        if (isset($path[0]) && in_array($path[0], supported_locales())) {
            $path[0] = $locale;
        }
        else {
            array_unshift($path, $locale);
        }

        return $scheme . '://' . $host . '/' . join('/', $path);
    }
}

web.php

use Facades\App\Managers\Localizer;

Route::group(['prefix' => Localizer::setLocale(), 'middleware' => 'web'], function () {
    // Note: as we set the prefix automatically, don't include it
    // in your routes, only the top most group.
    Route::view('', 'pages.home');
});