If you can only afford to localize for a few markets, pick the ones with strong revenue and a real ASO benefit from localization. Here is a sensible order based on Sensor Tower / data.ai aggregate revenue plus our own observations.
1. United States — English (US)
Largest revenue market. Already covered if you ship in English. Test variants here before localizing further.
2. China — Simplified Chinese (zh-Hans)
Largest user base. Distribution is not Apple alone — third-party Android stores matter. App names with both English and Chinese characters tend to perform best.
3. Japan — Japanese (ja)
Premium ARPU. Users prefer fully localized apps. Cute and information-dense screenshots outperform minimalist ones here.
4. Germany — German (de-DE)
Strong revenue and a market that punishes English-only listings. Watch out for long compound words; allow extra width.
5. France — French (fr-FR)
Cultural sensitivity matters. Avoid direct translation of US idioms. Use the formal "vous" in screenshots unless the brand is intentionally informal.
6. United Kingdom — English (UK)
Same alphabet as the US, but spelling and tone differ. "Color" becomes "Colour", "favorites" becomes "favourites". A separate UK locale is cheap and lifts conversion.
7. Korea — Korean (ko)
Trends move fast. Screenshots benefit from frequent refreshes. Hangul has unique spacing rules — do not auto-shrink fonts.
Beyond the top seven
Spanish (Mexico and Spain), Brazilian Portuguese, Italian, and Russian are the next tier. Add them once the top seven are stable and you have a localization workflow that does not eat your weekends.