Description:
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When using gettext($somestring), if $somestring could not be translated, it is returned without further translation. There should be a possibility to return a specific value if the string could not be translated instead. This impossibility is rather annoying when writing a sophisticated i18n system.

Reproduce code:
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// suggested solution:
$translated_text = gettext("some_string", true /* this optional parameter stands for "return false if text could not be translated" */);

if($translated_text === false) {
  echo "some_string could not be translated!\n";
} else {
  echo "some_string is $some_string in your favorite language\n";
}