German has two second persons. Your product should pick one.
Most tools translate “you” and leave the register to chance, which is how one screen says du and the next says Sie. Set it once per locale and every translation after it obeys.
It is not only German
Thirty-five languages carry an explicit rule. Everything else gets a careful generic instruction rather than a confident wrong one.
informal du
informal tu
informal tú
informal plain form
informal ty
informal 해요체
Two registers, one translation pass
A formal locale can be derived from its approved informal sibling rather than translated from scratch, so the wording you already signed off carries over and only the address changes.
Where the care shows
Archaic forms are flagged
Swedish ni and Danish De read as stiff or dated to a modern speaker. The rule knows, so the model is not told to use them.
It reaches the glossary
Terms you have fixed stay fixed regardless of register. A brand name is not more formal in the formal variant.
Never guessed
A language with no explicit rule gets a generic instruction. Vague and correct beats specific and wrong.
Set the register before the first translation
It is one field per locale, and it saves the pass where someone re-reads every screen.