Gettext_Translations::set_header( string $header, string $value )

	function set_header($header, $value) {
		parent::set_header($header, $value);
		if ('Plural-Forms' == $header) {
			list( $nplurals, $expression ) = $this->nplurals_and_expression_from_header($this->get_header('Plural-Forms'));
			$this->_nplurals = $nplurals;
			$this->_gettext_select_plural_form = $this->make_plural_form_function($nplurals, $expression);
		}
	}