Description:
------------
Trying to get the language name from the language code, I run

```
$bundle = \ResourceBundle::create('en_UK', 'ICUDATA-lang', true);
$lang = $bundle->get('Languages')->get('fr');
var_dump($lang);

$bundle = \ResourceBundle::create('en_US', 'ICUDATA-lang', true);
$lang = $bundle->get('Languages')->get('fr');
var_dump($lang);

$bundle = \ResourceBundle::create('en_foobar', 'ICUDATA-lang', true);
$lang = $bundle->get('Languages')->get('fr');
var_dump($lang);

$bundle = \ResourceBundle::create('en_NZ', 'ICUDATA-lang', true);
$lang = $bundle->get('Languages')->get('fr');
var_dump($lang);

$bundle = \ResourceBundle::create('en_AU', 'ICUDATA-lang', true);
$lang = $bundle->get('Languages')->get('fr');
var_dump($lang);
```
```
string(6) "French"
string(6) "French"
string(6) "French"
NULL
NULL
```

It returns `null` for Australia and New Zealand that indicates an Intl error of
> Cannot load resource element 'fr': U_MISSING_RESOURCE_ERROR"

The third parameter of `\ResourceBundle::create` functions is for call back that means it should fallback to its parent locale. Interestingly the [parent locale of `en_AU`][1] is `en_001`.

Similarly, this happens for currency names

  [1]: https://github.com/unicode-org/icu/blob/release-65-1/icu4c/source/data/lang/en_AU.txt

Test script:
---------------
$bundle = \ResourceBundle::create('en_AU', 'ICUDATA-lang', true);
$lang = $bundle->get('Languages')->get('fr');
var_dump($lang);

Expected result:
----------------
string(6) "French"


Actual result:
--------------
NULL