Cal.com's mission is to connect a billion people by 2031 through open-source scheduling infrastructure. Getting there requires serving users in every language – and for years, that requirement was a constant drag on engineering velocity.

The problem: always behind#

Cal.com had tried every standard approach. Crowdsourced translators through a translation management system. Localization agencies. Each added cost and coordination overhead, yet the result was the same: even top-priority languages were perpetually out of sync.

"We were always behind with internationalization," recalls Keith Williams, Head of Engineering. "Despite investing in agencies and crowdsourcing through translation management systems, even our top languages were out of sync. The costs were high and the manual work took our engineers away from building features."

The pattern is common. Legacy localization platforms manage human translator workflows – they don't eliminate the coordination overhead, they just organize it. Each release cycle meant another handoff to an external team, another wait, another round of review. The engineering team could ship a feature in a day; getting it localized could take two weeks.

The shift: localization as infrastructure#

In 2025, Cal.com deployed a localization engine on Lingo.dev. A localization engine is a stateful translation API: it persists Cal.com's product terminology, scheduling domain vocabulary, and per-locale configuration across every translation request. When the engine encounters "Workspace" or "Booking" in an English string, the glossary resolves the correct per-locale term before the model generates a single token.

The integration process required some initial adjustments given Cal.com's open-source codebase and contributor base. Lingo.dev's team worked through those directly.

"Their response times were insane," says Williams. "When we needed adjustments, they delivered fixes faster than I've seen from any vendor."

Results#

Once the localization engine was configured, Cal.com connected it to their CI/CD pipeline. Every code push triggers the engine; translations update automatically across all 36 languages.

• Engineering team no longer manages translation workflows
• All 36 languages stay synchronized with every release
• Significant reduction in localization costs compared to agency spend
• Zero handoffs – translations happen in the same pipeline as code deploys

"The best part? Our engineers don't even think about localization anymore," Keith explains. "They just build features, and translations happen automatically. It's exactly what we needed to make Cal.com accessible to everyone around the world."

What comes next#

Cal.com is extending the localization engine to cover email templates – the last remaining surface where translations were handled separately. When complete, every user-facing string in the product will flow through the same localization infrastructure.

For a team building toward a billion connections, the compounding effect matters: every glossary term configured today enforces correctly across every new feature, every new release, every new locale.