Translations: add an event/config value if messages should fallback to sourceLanguage

[Anubarak]

Edit: this is basically only a trainee problem as in "our trainees use Craft CMS wrong but it will be way to much effort to fix this now"

In your I18n class you have a check if the translated message is equal to the source message and in that case the message should be translated into the source language

cms/src/i18n/I18N.php

Lines 315 to 321 in bde0a7f

	// If $message is a key and came back identical to the input, translate it into the source language
	if ($translation === $message && !in_array($category, ['yii', 'site'], true)) {
	$messageSource = $this->getMessageSource($category);
	if ($messageSource->sourceLanguage !== $language) {
	$translation = parent::translate($category, $message, $params, $messageSource->sourceLanguage);
	}
	}

That means

{{ 'some translation'|t('my-custom-category') }}

Will basically never be rendered as it is in case the target language has no translation set, but the source language has.
This might not be a problem for English first projects, but for non English first developers.

When you have a site in language X and language En, where En is the default, but programmers use language X in their templates.

{{ 'jetzt starten'|t('my-custom-category', {}, 'de-DE') }}

Will always be translated into english unless the german version has a different translation. It would be awesome if there was an event to extend the categories that should not use a fallback.

It would be totally fine if it would be

!in_array($category, $this->someClassAttribute, true)

as well

[Anubarak]

Actually when I think about it... our trainees should rather learn to do it correclty... sorry for the disturbance