snipe-it/app/Http/Middleware/CheckLocale.php

<?php

namespace App\Http\Middleware;

use App\Helpers\Helper;
use App\Models\Setting;
use Closure;
use Illuminate\Http\Request;
use Illuminate\Support\Facades\Log;

class CheckLocale
{
    private function warn_legacy_locale($language, $source)
    {
        if ($language != Helper::mapLegacyLocale($language)) {
            Log::warning("$source $language and should be updated to be ".Helper::mapLegacyLocale($language));
        }
    }

    /**
     * Handle the locale for the user, default to settings otherwise.
     *
     * @param  Request  $request
     * @param  string|null  $guard
     * @return mixed
     */
    public function handle($request, Closure $next, $guard = null)
    {

        // Default app settings from config
        $language = config('app.locale');
        $this->warn_legacy_locale($language, 'APP_LOCALE in .env is set to');

        if ($settings = Setting::getSettings()) {

            // User's preference
            if (($request->user()) && ($request->user()->locale)) {
                $language = $request->user()->locale;
                $this->warn_legacy_locale($language, 'username '.$request->user()->username.' ('.$request->user()->id.') has a language');

                // App setting preference
            } elseif ($settings->locale != '') {
                $language = $settings->locale;
                $this->warn_legacy_locale($language, 'App Settings is set to');
            }

        }

        app()->setLocale(Helper::mapLegacyLocale($language));

        return $next($request);
    }
}