How to return validated value of ID in Laravel validation

So I have created looped generated radio-buttons:

<div class="custom-control custom-radio guest-form">
    @foreach(config('const.res_site') as $id => $res)
    <div class="form-radio">
        <input class="custom-control-input" type="radio" onchange="otherResSite()" id="" value="" 
            name="reservation_site" >
        <label for="" class="custom-control-label"></label>
    </div>
    @endforeach
    <div class="otherField" id="ifOtherSite" class="otherSite" style="display: ">
        <input type='text' class="form-control" id='otherSite' name='otherSite' value=""><br>
    </div>
</div>
@if ($errors->has('otherSite'))
    <div class="form-group">
        <p class="text-danger"></p>
    </div>
@endif

const.php

'res_site' => [
    0 => 'site1',
    1 => 'site2',
    2 => 'other',
],

This one is to validate the otherSite value if selected option is other. It now works well but the validation message returned is like this:

The other site field is required when reservation site is 2.

My validator is like this:

return [
    'reservation_site' => ['required'],
    'otherSite' => ['required_if:reservation_site,2'],
]

Now, how can I make its return message as

The other site field is required when reservation site is other

Is there any way I can do that?

via Chebli Mohamed