Snippets for the article: https://hookturn.io/singular-or-pluralised-string-wordpress/

pluralise-string-based-on-variable-with-sprintf-and-acf.php

<?php

// Use an ACF field value to pull the number from the database.
$number_of_items = (int) get_field('my_numerical_field', $post_id );

$string = sprintf( 
	_n(
		'%d item in stock',
		'%d items in stock',
		$number_of_items
	), 
	$number_of_items 
);

pluralise-string-based-on-variable-with-sprintf.php

<?php

// Combine it with sprintf() to dynamically show the exact 
// number of items in the resulting string.
$string = sprintf( 
	_n(
		'%d item in stock',
		'%d items in stock',
		$number_of_items
	), 
	$number_of_items 
);

pluralise-string-based-on-variable.php

<?php

// Display a string in either singular or plural form depending 
// on the number of items. _n() is a translation function so this
// will also translate where a translation is available.
$string = _n(
	'item',
	'items',
	$number_of_items
);