Spell out numbers not shown when arithmetic problem disabled

Hi Viktor,
thank you for the implementation of the Spell out numbers feature within the Captcha extension. Despite, I cleared the website +browser cache, it looks like the numbers are not shown within the text field box by default.
When both the arithmetic problem & spell out number feature toggles are selected/enabled, it still shows only the text info: "ten + twelve" rather than their number representation. When disabling the arithmetic problem toggle and leaving the spell option enabled on the front-end, nothing is loaded. Perhaps it helps to make some verification that when it is not supported to show a message in the backend as having a fail back option to toggle the arithmetic problem toggle?
Perhaps this is mentioned like: "if the NumberFormat class is available in PHP"? I use PHP v8.3. Thank you for the support.