The first parameter is not the language, but the separator.

You can use named parameters to specify a language while using the default separator:

$ php artisan tinker
Psy Shell v0.12.7 (PHP 8.2.27 — cli) by Justin Hileman
> str('nad')->slug(language: 'az')
= Illuminate\Support\Stringable {#6612
    value: "nad",
  }

> str('nad nad')->slug(language: 'az')
= Illuminate\Support\Stringable {#6637
    value: "nad-nad",
  }

@rodrigopedra But it does not explain how is str('nad')->slug(separator: 'az') equal to nazd

This line here, on the Str@slug() method, does this odd behavior:

When the separator has more than one character, all of its characters are added to the regular expression's character class.

So the expression on the line above will evaluate to:

preg_replace('![az\s]+!u', 'az', 'nad')

Which means it will replace any letters a, z, or any blank characters (\s), by the sequence az (the separator).

Thus, as nad has a a character, this gets replaced by az, then becoming nazd.

You can try with this simple script:

<?php

$title = 'nad';
$separator = 'az';

$title = preg_replace('!['.preg_quote($separator).'\s]+!u', $separator, $title);

echo $title, \PHP_EOL;

One could propose a PR to assert a separator only has a single character.

On the other hand, people could be relying on the current behavior to generate strings like this:

$ php artisan tinker
Psy Shell v0.12.7 (PHP 8.2.27 — cli) by Justin Hileman
> str('PHP is great!')->slug('-=-')
= Illuminate\Support\Stringable {#6609
    value: "php-=-is-=-great",
  }

Multiple characters might not be a problem, as long as they are proper delimiters 🤔

The first parameter is not the language, but the separator.

You can use named parameters to specify a language while using the default separator:

$ php artisan tinker
Psy Shell v0.12.7 (PHP 8.2.27 — cli) by Justin Hileman
> str('nad')->slug(language: 'az')
= Illuminate\Support\Stringable {#6612
    value: "nad",
  }

> str('nad nad')->slug(language: 'az')
= Illuminate\Support\Stringable {#6637
    value: "nad-nad",
  }

Oh, you're right. I don't remember when I last used this method, until now (wrote it once in Sluggable trait, where I passed all arguments, and that's all). I didn't even notice that I should pass language as the second argument. An outside perspective always helps :)

@rodrigopedra But it does not explain how is str('nad')->slug(separator: 'az') equal to nazd

Yeah, maybe if it worked like expected, without any replace, because the input doesn't have any spaces, it would help me to notice the source of the issue.

By the way, please note that the method is only designed for single-character separators, mainly due to the regex character classes.

I considered suggesting support for multi-character separators, but it would be somewhat difficult to implement because of the negated character class (here). There are various ways to solve this, but it would complicate the code, and I don't think it would be worth it.

To add some robustness, we could throw an exception if the provided separator is longer than one character.

I attempted this implementation of multi-character separators, and as expected, it made the code more complex, harder to understand, and more prone to regression. Therefore, I reaffirm that it is not worth pursuing.

Just as a reminder, the second argument of the final trim() (here) is a list of characters.