German translation is out of date.

http://php.net/manual/de/function.substr.php

This bug has been fixed in the documentation's XML sources. Since the
online and downloadable versions of the documentation need some time
to get updated, we would like to ask you to be a bit patient.

Thank you for the report, and for helping us make our documentation better.

When you like to see this issue as documentation (translation) problem instead of a bug at http://php.net/manual/de/function.substr.php and think it could be easily solved by just changing the default value for argument $start, then I'd like insist that the documentation will show the different version behaviors, for example like this:

<?php
var_dump(substr('a', 1)); // bool(false) if php version < 7
var_dump(substr('a', 1)); // string(2)"" if php version >= 7
?>

In my option it still seems more a bug than a desired behavior. I see no value in this new behavior for php7, but may be you can change my mind.

Until the online docs are updated with @cmb's change, look at the English version.
http://php.net/manual/en/function.substr.php

- The Changelog specifically states what changed.

- Example #4 shows the behaviors of substr with different inputs. Part 6) shows what happens if you call the function with $start == strlen($string), and shows it both for PHP 7 (empty string) and for PHP 5 (false).

- The Errors/Exceptions example shows it returning false with $start=2 (beyond the end of the string) instead of $start=1 (at the end).

Is that enough to show that the behavior has changed with PHP 7?

Yes, it's much better now. Thanks a lot.