Work only setDefaultLocale()

and it should work without any default settings it should be english.

it does not find the translation in 'en-US', and tries to get from defaultLocale

umm

if you don't have a translation you shouldn't throw any exceptions.

for example my app is in english, and by default this is setting the translatorinterface will throw error.

for example, if I have a Russian version by default, where the translation is 100%, and there is another language, where 50%, and if I only use setLocale, then 50% of the site will not be translated, and so I set setDefaultLocale to Russian and then already you can use setLocale Kazakh or another language, and which does not have a translation, it will be displayed in Russian

when configuring, you need to use setDefaultLocale, in applications you need to use setLocale

You don't understand me, for example if I configure TranslatorInterface and I don't have any translations because the Validator is going to throw an exception it doesn't make sense to me, so I have configured it.

It is like configuring the logger and if I don't use it it will throw an exception.

$container->set(
           TranslatorInterface::class,
           function (ContainerInterface $container) {
               $translator = new Translator(
                   $container->get(EventDispatcherInterface::class),
                   new MessageTranslator([]),
                   null
               );

               $translator->setDefaultLocale('en-US');

               return $translator;
           }
       );
and when you need to change to another language in middleware or controller or somewhere else, use setLocale

maybe I don't understand the essence of the problem, you are not using a translator, but it throws an error?

yes

setting translatorinterface and validator throw error

if you pass the translator to ValidateFactory, then it will try to translate and take defaultLocale if the locale is not set or there is no translation for it, since defaultLocale is not valid, it throws an exception, it is strange why the system Locale returns an invalid locale, or the regexp  is not correct...

I think it should be reviewed

what exactly ?, the logic of the translator?

If the locale part, more evidence should be added when no locale exists.

Because if I don't configure any, it takes the one from the machine.

And I think it should be English by default.