?ContainerInterface?

after locale change -> in different locale?

Hmm, is there any way we can get rid of those parent calls?

I've been trying to come up with better solution, but without success. If you have any suggestion, please share with me 😃

Hardcoded en_US?

This will filter out 0.

Strict types can be added here (and to this class entirely)

Missing typehint

Can be private

Filtering out zeros.

What happens if values[attribute.value][fallbackLocale] is not defined?

array_search returns either a key (int / string) or false when the value was not found, so this expression can be reduced to $localeCode === $key only.

Why is it so? Empty treats 0 value as empty.

$newKey cannot be null here as getUniqueKey returns string.

Missing typehints here (+ other method definitions).

SelectAttributeChoicesCollectionType uses LocaleProviderInterface::getDefaultLocaleCode() to get its default locale, this one has base locale injected as $defaultLocale, is that intentional?

Anyway, if it's intentional, I guess $baseLocale would be more appropriate name then.

I guess there's still something wrong with those definitions, %locale% points to a base locale code, whereas sylius.translation_locale_provider service has getDefaultLocaleCode method which returns current channel's default locale. Is there any reason for using these two simultaneously instead of only one of them?

I didn't notice that 👍
I've changed to use sylius.translation_locale_provider instead of %locale%.