Holafly

Holafly is a leading international eSIM provider dedicated to bringing peace of mind to travelers worldwide. By offering seamless mobile connectivity in over 200 destinations with an outstanding 4.7/5 on Trustpilot, Holafly enables travelers to navigate new cities, book late-night rides, and stay in touch with family without worrying about roaming fees. Today, Holafly connects over 2 million monthly active users across iOS, Android, and the web, with more than 25 million eSIMs sold.

As Holafly grew, maintaining separate native Android and iOS applications became an operational bottleneck. With two separate teams working in silos on distinct codebases, delivering new features was slow and resulted in frequent discrepancies between platforms. To accelerate feature delivery and ensure a consistent user experience, Holafly sought a unified cross-platform framework.

Why Flutter? Unifying Global Mobile Engineering and Accelerating Delivery

Holafly chose Flutter to break down team silos and unify their mobile engineering under a single codebase. Rather than attempting a slow, piecemeal transition, the team took a bold approach: rebuilding their existing native apps entirely in Flutter. Remarkably, the team completed the full rewrite in just three months. The Flutter app performed so well in testing that Holafly retired their legacy native codebases and released the Flutter app directly to production.

Beyond development velocity, Flutter transformed how Holafly's engineering team collaborates. With engineers distributed around the globe (including Uruguay, Argentina, Italy, and Germany), working on separate native codebases had created isolation. Adopting Flutter allowed the entire international engineering team to collaborate seamlessly on the same codebase, drastically streamlining code reviews, sprint planning, and knowledge sharing across time zones.

Building with Flutter: Type-Safe Platform Channels and Modular Architecture

Holafly's application relies on deep platform-level integration for eSIM installation, real-time data consumption tracking, and managing multiple eSIMs for travelers hopping between countries. Because each operating system exposes different APIs for eSIM profiles and cellular network management, the team built standalone modular packages that encapsulate platform-specific logic. To establish seamless, type-safe communication between Flutter and the underlying native iOS and Android platform code, Holafly integrated Pigeon. By generating type-safe platform channel code, Pigeon enables developers to call clean, single-method Dart APIs without writing manual serialization or managing platform channel boilerplate.

To support scalability and future development, Holafly architected their project as a monorepo. They divided functionality into distinct, modular packages with clearly defined public interfaces. This architecture enables any engineer on the team to consume or contribute to a package without having to navigate its internal implementation details. These standalone packages can also be reused directly across future internal applications.

Localization is vital for Holafly's global user base, as the app must speak each traveler's native language. Holafly upgraded their localization pipeline across 20+ languages by pairing Flutter's internationalization support and Application Resource Bundle (.arb) files with Gemini and the Crowdin Flutter SDK. Because the ARB format natively supports metadata, contextual descriptions, parameter definitions, and examples, it provides Gemini with the rich context necessary to generate accurate, culturally grounded translations. This integration made Holafly's localization process faster, simpler, and substantially less prone to errors.

Key results and business impact

By transitioning to Flutter, Holafly achieved remarkable development velocity and scaled their global reach:

• Shipped in 3 months: Rebuilt the full native application and deployed the new Flutter version directly to production in only three months.
• Rapid global scale: Scaled to over 2 million monthly active users across iOS, Android, and web.
• Unified global team: United a distributed engineering team across five countries (Uruguay, Argentina, Italy, and Germany) on a single, collaborative codebase.
• Native performance with Pigeon: Built modular packages for eSIM management using Pigeon for type-safe platform communication, preserving native performance with clean Dart APIs.
• AI-driven localization with Gemini: Automated internationalization across 20+ languages using Flutter ARB files, Gemini, and the Crowdin Flutter SDK, accelerating translation while reducing errors.