Most legacy mobile apps weren’t designed with localization in mind. Strings are hardcoded, layouts are tightly fit to English, pluralization is inconsistent, and there’s little to no validation around translated files. When teams decide to go global, localization can feel risky enough to require a rewrite or a feature freeze. This guide shows a safer alternative. It walks through how to localize an existing iOS or Android app incrementally by scoping carefully, externalizing strings over time, and planning for layout expansion, plurals, and placeholders early. It also explains why treating localization as a continuous process — instead of a one-time project — dramatically reduces risk as apps scale to more languages. The goal isn’t perfect localization on day one, but a workflow where adding the next language feels predictable and boring, not fragile or disruptive.