French-language layout not planned from the start
French text averages 15 to 20 percent longer than its English equivalent. A navigation item that reads "All Collections" in English becomes "Toutes les collections" in French. A product page heading that fits neatly at 300px in English overflows or wraps awkwardly in French if the layout was built for English word lengths. A redesign that starts in English and adds a French translation at the end discovers these problems in QA or, worse, after launch. The correct process designs bilingual layout from the start — designing the French version in parallel with the English version during the wireframe and component design phase, not as a secondary pass. This requires the designer to work with French copy at the layout stage, which means the French translation needs to be available before design is finalised, not after development is complete.