$router->map('GET','/th/work/sample', 'work/sample.php', 'sample', 'th');
But this fifth option is not available. Is there a workaround for this?
This is because the map function simply does not support the fifth parameter.
public function map($method, $route, $target, $name = null)
Source code AltoRouter.php: map
You can call the match function, which goes along the original route, if you can somehow intercept and make your code work up to the router. The match function returns the name of the route. But that means you create named routes for each language, and then you begin to understand the solution provided by @gbe
$router->map('GET', '/[:lang]/work/sample', 'work/sample.php', 'sample')
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