function prefix_pronamic_datetime_default_format( $format ) {
	return _x( 'D j M Y \a\t H:i', 'default datetime format', 'pronamic-ideal' );
}

add_filter( 'pronamic_datetime_default_format', 'prefix_pronamic_datetime_default_format' );

It is important to note that date_i18n():

1. does not have full feature parity with date(), not all formats are supported (such as shorthands);
2. does not accept Unix timestamp (despite documented to), the expected value is “WordPress timestamp” (offset by time zone);
3. has issues with certain timezone settings, such as numerical ones;
4. does nothing with $gmt argument under normal circumstances;

Any use of this function must be carefully audited for correctness, especially in regards to output of time zones.

Source: https://developer.wordpress.org/reference/functions/date_i18n/#comment-2403

• https://github.com/woocommerce/woocommerce/blob/3.3.5/includes/class-wc-datetime.php
• https://github.com/Rarst/wpdatetime