Translation of "Unsubscribe…" impossible

I haven't ever used multiple languages in Drupal, so my ability to help is limited. What I can do is search the code...

In simplenews.module we have the message you describe perfectly isolated:
$variables['unsubscribe_text'] = t('Unsubscribe from this newsletter', [], ['langcode' => $variables['language']]);

The longer message with complex syntax comes from simplenews-newsletter-body.html.twig and it has no text that needs translating:

{% if not opt_out_hidden %}
    {% if format == 'html' %}
        <p class="newsletter-footer"><a
                    href="[simplenews-subscriber:unsubscribe-url]">{{ unsubscribe_text }}</a>
        </p>
    {% else %}
        -- {{ unsubscribe_text }} : [simplenews-subscriber:unsubscribe-url]
    {% endif %}
{% endif %}

So everything seems correct in the code. I believe you don't need to translate the part that has a red line around it in your screenshot. The translation system has somehow combined together two things and asked you to provide a translation. One of them you already translated, the other has no translatable text.

Sounds reasonable -- I cannot see the second field in other installations. Gremlins …

Automatically closed - issue fixed for 2 weeks with no activity.

I have the same problem in french. Impossible to have the translation....