Magento\Framework\Stdlib\DateTime\TimezoneInterface broken for English(United Kingdom) locale

[gwharton]

Preconditions

1. Magento CE 2.1.8 bog standard, updated with composer update
2. Locale set to English (United Kingdom)
3. Timezone set to Europe/London

Steps to reproduce

1. Run the following code

        $date1 = $this->datetime->date();
        $output->writeln(print_r($date1,true));
        $date2 = $this->timezone->date($date1);
        $output->writeln(print_r($date2,true));

Expected result

1. $date1 should be UTC time
2. $date2 should be an array with time set to local time, in this example UTC+1

Actual result

Set locale to English (United Kingdom)

2017-08-25 15:48:00
DateTime Object
(
    [date] => 2031-02-07 15:48:00.000000
    [timezone_type] => 3
    [timezone] => Europe/London
)

Set locale to English (United States)

2017-08-25 15:46:40
DateTime Object
(
    [date] => 2017-08-25 16:46:40.000000
    [timezone_type] => 3
    [timezone] => Europe/London
)

[gwharton]

The module I used to prove concept can be downloaded from

TestTimeZone.zip

It can be invoked by

php bin/magento testtimezone:run

[gwharton]

Possibly related to #10580

[magento-engcom-team]

@gwharton thank you for your bug report.
We've created internal ticket MAGETWO-75374 to track progress on the issue.