How to Localize iOS and macOS Apps

Published on August 27, 2025 by

When developers finish building an app for iOS or macOS, they often feel like the hard work is finally over. The code runs smoothly, the interface looks polished, and the first round of testers are happy. Then someone drops the dreaded question: “But what about localization?” That’s when the mood shifts, because localization is rarely the glamorous part of app development. It’s essential though, and skipping it is a surefire way to limit your app’s reach.

Localization is more than translating words from English to French, Spanish, or Japanese. It’s about adapting the entire experience so users feel the app was built for them from the start. People notice the details—dates that follow local formats, currencies that match their wallets, and even images that resonate with cultural expectations. In a global market, an app that feels “foreign” creates friction, and friction drives people to uninstall. Developers who want international success have no choice but to take localization seriously.

Now, let’s be honest. I once thought localization was as simple as running strings through Google Translate. A few hours later, I realized that my app greeted German users with phrases that looked like someone swallowed a dictionary and spat it back out. That experience taught me one thing: you need a process, not a quick fix. Apple provides tools, but you also need planning, testing, and a sense of cultural nuance.

So, let’s break down how to localize iOS and macOS apps properly. It’s not rocket science, but it does require attention to detail and, occasionally, a sense of humor when things go wrong.

Understanding Localization vs. Internationalization

Before diving into the how, it’s worth clearing up the what. Developers sometimes confuse internationalization and localization. Internationalization, often shortened as i18n (yes, the “18” represents the letters between the first and last characters), is about preparing your app so it can be localized. Localization, or l10n, is the process of actually adapting it for specific markets.

Think of internationalization as laying the foundation for a house. If you forget to pour the concrete correctly, painting the walls later won’t help. Internationalization ensures your code can handle different languages, text lengths, character sets, and formats. Localization, on the other hand, is putting up the wallpaper, installing furniture, and making it feel like a real home.

One mistake developers make is skipping internationalization altogether. They hardcode English text, assume dates will always use month/day/year, and never test with right-to-left languages. By the time they decide to localize, the foundation is cracked, and the fix is painful. Trust me, retrofitting is worse than doing it right the first time.

Apple’s Built-In Localization Tools

Apple, to its credit, makes localization easier than many platforms. Both iOS and macOS support a framework called Foundation, which includes powerful features for handling dates, numbers, and text in multiple languages. You don’t have to reinvent the wheel; you just need to learn how to use the one Apple already built.

The core feature is Base Internationalization. With it, you store your app’s user-facing text in .strings files. Instead of hardcoding labels into your interface, you reference keys that point to localized values. For example, “WELCOME_MESSAGE” might map to “Welcome” in English, “Bienvenue” in French, and “Willkommen” in German. When the system detects the user’s language preference, it displays the right string automatically.

In Xcode, adding localization support is a matter of a few clicks. You enable Base Internationalization, select the languages you want to support, and generate the appropriate .strings files. The trick, however, is keeping those files consistent and ensuring translators understand the context. I once sent a .strings file to a translator with the word “Charge” in it. They asked me: “Do you mean charge money, charge a battery, or charge into battle?” Lesson learned—context matters.

The Localization Workflow

Localization is not a one-time task. It’s a workflow that repeats whenever you add new features, update UI elements, or expand to more markets. A solid workflow saves your sanity and ensures your app doesn’t end up with half-translated menus.

Here’s a practical step-by-step process:

Identify Localizable Content
Extract all user-facing text, images, and media that may need adaptation. Avoid leaving hidden English words in your UI.
Use Xcode’s Export Function
Xcode allows you to export .xliff files, which translators love because they include context and structure.
Collaborate With Professional Translators
Machine translation is fine for testing, but professional translators prevent embarrassing mistakes. Remember my “Charge” disaster? Exactly.
Integrate Localized Assets
Import the translated .xliff back into Xcode and ensure all languages are included.
Test in Simulator and Devices
Change your device language to confirm everything displays properly. Watch out for text expansion in German or French—it can break layouts.
Iterate Frequently
Whenever you push an update, run through the workflow again. Consistency keeps your app polished.

Skipping any step usually leads to chaos. And chaos in production is like a raccoon in your kitchen—funny for a moment, but painful to clean up.

Handling Dates, Numbers, and Currencies

Text is only half the story. Dates, numbers, and currencies are equally important for localization. Apple’s DateFormatter and NumberFormatter classes handle much of the heavy lifting. With the right locale settings, you can automatically display dates as 12/31/2025 for US users and 31/12/2025 for Europeans.

Currencies are trickier because they involve both formatting and conversion. If your app displays prices, don’t just slap a currency symbol next to a number. Use NumberFormatter with .currency style, and let the system decide how to display it. Otherwise, you’ll end up with oddities like “100 USD$,” which looks like a bad knockoff product on a shady website.

Testing matters here too. Developers often forget that some countries use commas instead of periods for decimals. Showing 1,000.50 in one locale and 1.000,50 in another isn’t a bug—it’s expected. If you don’t plan for it, though, your accounting feature might look like a riddle.

Dealing With Right-to-Left Languages

One of the trickiest parts of localization is supporting right-to-left (RTL) languages such as Arabic and Hebrew. If your layout assumes left-to-right, you’ll face broken interfaces. Apple helps by letting you use Auto Layout and leading/trailing constraints instead of hardcoded left and right. This way, the system automatically flips the layout when needed.

I remember testing an app in Arabic and laughing nervously as the buttons stacked on top of each other like a game of Tetris gone wrong. The fix was simple: use system conventions rather than hardcoded positions. Moral of the story? Never underestimate the chaos RTL can bring if ignored.

Localizing Images and Media

Text is the obvious candidate for localization, but images, icons, and media may also require changes. For instance, an image showing dollar bills may not resonate with Japanese users. Similarly, a “thumbs up” icon might have unintended cultural meanings elsewhere.

Apple allows you to create localized asset catalogs. Within Xcode, you can include different versions of the same image for different locales. When users switch languages, the system automatically loads the right asset.

Sometimes the change is subtle, like switching the text on a button inside an image. Other times, it’s major, like creating an entirely different tutorial video. The more effort you put into tailoring media, the more your users will feel at home.

Testing and QA in Localization

Testing localization is a discipline of its own. It’s not enough to switch your device language and call it a day. You need to test with multiple languages, varying text lengths, and actual users from the target regions.

Apple provides pseudo-localization options. This mode exaggerates text length and inserts accented characters, helping you spot layout issues before a real translation is added. It’s like a stress test for your UI.

In addition to pseudo-localization, involve real users in beta testing. Nothing beats feedback from people who live in the culture you’re targeting. They’ll spot oddities that developers and translators miss. For example, a phrase that’s technically correct might sound robotic in everyday conversation.

Common Pitfalls to Avoid

Developers often make the same mistakes when localizing apps. Here are a few to keep in mind:

Hardcoding text instead of using .strings files.
Forgetting to test with right-to-left layouts.
Ignoring pluralization rules (English plurals are simple, but Slavic languages get wild).
Assuming images are universal across cultures.
Not budgeting time or money for proper translation.

I’ve personally fallen into at least three of these traps. The good news is that once you know the pitfalls, you can actively avoid them.

Why Localization Pays Off

Yes, localization takes time and money. But the payoff is significant. The App Store is a global marketplace, and users are more likely to download and engage with apps in their own language. Studies repeatedly show that people trust localized products more and are willing to pay for them.

From a competitive standpoint, localization can be the difference between dominating a market and fading into obscurity. If your rival supports Spanish and you don’t, guess who gets the attention of 500 million Spanish speakers? It’s not rocket science—it’s just common sense.

Conclusion: Making Localization Part of Your DNA

Localization is not an optional extra for iOS and macOS apps. It’s a core part of building a product that resonates globally. Developers who treat localization as an afterthought will always play catch-up. Those who embrace it from the start will reap the rewards of a broader audience and stronger user loyalty.

The key is to approach localization as a process, not a one-off project. With Apple’s tools, professional translators, and a consistent workflow, you can build apps that feel native in any market. Add in testing and cultural awareness, and you’ll be well ahead of the competition.

At the end of the day, localization is like good manners. People notice when you make the effort, and they appreciate it more than you think. Build apps that speak to users in their own language, and they’ll repay you with loyalty.

And remember—if all else fails, don’t rely on Google Translate to save the day. Unless, of course, you enjoy seeing your app accidentally greet users with “Battery Charge Attack.”