eval_test.php

<?php

echo myMessage("WELCOME", "win3zz", 0);

function myMessage() {

	$messages = [
    "WELCOME" => "Welcome, %s! You have %d new messages.",
    "ERROR" => "An error occurred: %s"
    ];

	$numargs = func_num_args();
	$args = func_get_args();
	$messagename = $args[0];

	if (@array_key_exists($messagename, $messages)) { $string_with_percents = $messages[$messagename]; }
	else { return "MESSAGE NOT FOUND"; }

	$sprintf_argument = "\$translated_string = sprintf(\$string_with_percents";
	for ($i=1; $i<$numargs; $i++) {
		$sprintf_argument .= ",  @htmlentities(\$args[$i], ENT_QUOTES)";
	} 
	$sprintf_argument .= ");";

	eval($sprintf_argument);

	return $translated_string;
} 
?>