How to remove character that is not a letter in a string?

You can use preg_replace to remove characters that are not letters from a string . Then you can combine it with array_map .

$callback = function ($value) {
    return preg_replace('/\W+/u', '', $value);
};

array_map($callback, $array);

I used the u f modifier to recognize accented characters.

The expression \W+ means any character other than words .

In Unicode, the first accented Latin letter has the code \u00c0 ( "À" / a>) and the last one is \u024F ( " and "). You can select all letters using the basics ( a-zA-Z ) and the range between those two special characters. So:

[a-zA-Z\u00C0-\u024F]

And because brackets are bracketed, denial is easy:

[^a-zA-Z\u00C0-\u024F]

Now just apply. You can try it on the browser console:

"Açaí, lingüiça, outras comidas acentuadas etc.".replace(/[^a-zA-Z\u00C0-\u024F]/g, "");

Note that this also removes spaces and punctuation. Add a space in the brackets if you want to preserve spaces between words, commas and periods if you want to keep score etc.