Feature: Readability score in RTE overlay 

Description 

The DeepL Write RTE overlay now displays a Flesch reading-ease score for both the original and the optimized text, giving editors immediate feedback on how readable a text is before and after rephrasing.

The score is shown as a coloured marker bar above each text area and is updated for the optimized text once the rephrasing result is returned.

Readability is calculated per content language using a language specific Flesch reading-ease formula. German, English, French, Italian and Portuguese are supported out of the box, and regional variants such as en-US or pt-BR are matched by their primary language subtag. For unsupported languages or empty texts no score is reported and the overlay keeps working without interruption.

Impact 

Editors using the DeepL Write overlay in the rich text editor get an at-a-glance readability indication for the text they are working on, helping to judge whether a rephrasing actually improves readability.

Developer 

The readability score is computed by small, language specific calculators. Each calculator implements ReadabilityCalculatorInterface (usually by extending AbstractReadabilityCalculator) and is registered through the deepl.readability service tag. At runtime ReadabilityCalculatorRegistry selects the calculator whose language matches the primary subtag of the editor content language.

Out of the box the following languages are provided, each using a documented Flesch reading-ease adaptation, where ASL is the average sentence length (words / sentences) and ASW the average number of syllables per word (syllables / words):

• English (en) — Flesch: 206.835 - 1.015 * ASL - 84.6 * ASW
• German (de) — Amstad: 180 - ASL - 58.5 * ASW
• French (fr) — Kandel & Moles: 207 - 1.015 * ASL - 73.6 * ASW
• Italian (it) — Franchina & Vacca: 206 - ASL - 65 * ASW
• Portuguese (pt) — Martins et al.: 248.835 - 1.015 * ASL - 84.6 * ASW

<?php

declare(strict_types=1);

namespace Vendor\MyExtension\Readability\Calculator;

use Symfony\Component\DependencyInjection\Attribute\AutoconfigureTag;
use WebVision\DeeplWrite\Readability\Calculator\AbstractReadabilityCalculator;

#[AutoconfigureTag('deepl.readability')]
final class FleschReadingEaseSpanish extends AbstractReadabilityCalculator
{
    // Primary language subtag matched against the editor content language.
    protected const LANGUAGE = 'es';

    // Locale of the org_heigl/hyphenator dictionary used for syllables.
    protected const HYPHENATION_LOCALE = 'es';

    protected function calculateScore(
        float $averageSentenceLength,
        float $averageSyllablesPerWord,
    ): float {
        // Return the language specific Flesch reading-ease score; the base
        // class guards empty input and caps the result at the maximum of 100.
        return 206.84 - 1.02 * $averageSentenceLength - 60.0 * $averageSyllablesPerWord;
    }
}