problem with dash character in the Laravel routing

I have this code in my route:

Route::get('/{lang}/post/{id}-{slug?}',function($lang, $id, $slug=null) {
    dd($lang, $id, $slug);
})->where('id', '[0-9]+');

site.com/en/post/30 -> Work

site.com/en/post/30-myslug -> Work

site.com/en/post/30- -> 404

Why I get a 404 error? slug is optional.

If I replace the dash with another character for example 'i'

Route::get('/{lang}/post/{id}i{slug?}',function($lang, $id, $slug=null) {
    dd($lang, $id, $slug);
})->where('id', '[0-9]+');

site.com/en/post/30i Work

Is there any limitation for the dash character?

Laravel 5.8

Sincerely

via Chebli Mohamed