English is a compact language and designing in it first is a trap. "Down payment" becomes "aanbetaling"; "Total interest" becomes "Gesamtzinsen"; a label that fit neatly in its box now wraps, truncates, or pushes the input off the edge of a 375-pixel screen. German runs roughly 30% longer than English; Dutch is close behind.
The fix is not translating shorter. Compressed labels read like a form filled in by a robot, and this site's voice — dry, specific, written by a person — is worth keeping in every language.
What actually survives
Three habits. No fixed-width text containers, anywhere: labels size to their content and layouts flex around them. Every layout is checked with the longest translation we have, not the English. And numbers, dates and currency are formatted by the browser's own locale machinery rather than by hand — the same code that writes $1,234.56 for a US visitor writes € 1.234,56 for a Dutch one, decimal comma included.
The practical test is blunt: paste the German labels into the mortgage calculator at 375 pixels and see what breaks. When the answer is nothing, the layout is done.