Du wirst sehen.

Here is another sentence where the plural and the singular form of the Spanish verb is given as a translation for the singular verb in German. Since I have seen this several times, I think there must be something I need to learn about either German or Spanish that makes this correct. I hope someone can explain it to me. I see “Du wirst sehen” and I think “Verás” (second person, singular, informal). If I see “Ihr werdet sehen” then I would think “Veréis” (second person, plural, informal in Spain) or “Veran” (second person, plural, both formal and informal in Latin America). Is my German knowledge out of date? Are Germans now using “Du wirst …” for second person, plural, informal as well as for second person, singular, informal?