Senior Software Engineer, Internationalisation Platform in London

At Klaviyo, we value the unique backgrounds, experiences and perspectives each Klaviyo brings to our workplace each and every day. We believe everyone deserves a fair shot at success and appreciate the experiences each person brings beyond the traditional job requirements. If you’re a close but not exact match with the description, we hope you’ll still consider applying.

Why You Should Join the Internationalisation Platform Team

The i18n Platform team owns all the ways we create, process and deliver internationalisation features for our users at Klaviyo. As a Senior Software Engineer, you will be a key contributor and mentor leading complex, multi-component projects across the i18n platform. You will be involved in how we manage translations, deliver new localisation features, handle multiple currencies, and improve our internationalisation processes. You can look forward to being a part of a highly technical team with significant domain expertise. We oversee tools and services that are leveraged across the organization from the frontend UI to backend data. The team also owns and orchestrates several services to manage the pipeline of translations with our localisation team. As we look toward the next 6-12 months, we aim to focus on delivering LLM workflows to improve our translation capabilities, increase the availability of our Smart Translations product, and develop new features for handling different currencies in multiple regions.

Why you should join

• We foster a culture of psychological safety, collaboration, and work/life balance through flexible hours and structured on-call rotations.
• We practice a “you make it, you support it” attitude to our products and provide on‑call support in case of incidents.
• We offer compensation for on‑call rotations and expect to maintain a very low number of incidents requiring call‑out.
• New engineers are onboarded to the on‑call rotation gradually, typically joining the active rotation after their first 6 months and thorough training.
• We are committed to your growth. You will be paired with a dedicated mentor and given time for focused skill development, including opportunities to attend relevant industry conferences and a growing suite of learning & development opportunities.
• We enjoy a high degree of autonomy to generate innovative solutions across the entire system, learning directly from customers and suggesting cool new approaches.
• Free lunch at our Aldgate office three times a week.
• Highly competitive salary, equity package, and comprehensive health benefits.

How You Will Make a Difference

• You will lead and drive the design and execution of complex, business‑critical projects across the Internationalisation platform.
• You will be responsible for implementing new functionality and establishing design patterns for complex, multi‑component systems.
• You will take full lifecycle ownership of features and projects, driving requirement refinement and setting the pace for all phases of execution.
• You will proactively collaborate with cross‑functional partners to influence product requirements and communicate technical needs to other teams.
• You will be an active participant in all team processes and accountable for meeting the health and operational excellence (SLOs) of your area of ownership.
• You will help interview new engineering team members and actively mentor junior engineers in your product area.

What we are looking for

• A strong interest in internationalisation, localisation, and translation.
• A desire to serve our international customers and expand Klaviyo’s capabilities.
• 5+ years of demonstrable experience delivering high‑quality, customer‑facing software.
• Deep understanding of complex systems (or similar large‑scale distributed systems) and strong systems thinking, with a proven ability to scale, observe, and maintain services.
• Familiarity with full stack development concepts and a strong aptitude to learn.
• Experience working with both monolithic and microservices architectures.
• Experience with database design that can withstand high query volumes.
• Experience debugging performance issues and improving application performance.
• An interest and aptitude for collaboration across teams and disciplines.
• An understanding of challenges in developing software across multiple languages and catering to non‑English speaking users.
• Thrives in a fast paced, customer focused, and strategic environment.
• A track record of prioritizing the needs and success of the company overall above the immediate needs of the team.

Nice to Have

• Proven experience with large‑scale system design and driving the technical/architectural evolution of a product area.
• Experience with AWS or any similar cloud provider.
• Experience with billing systems in multiple currencies.

Technologies we use (not exhaustive)

• React, TypeScript, JavaScript, HTML, CSS
• Babel, Webpack, Eslint, Prettier
• REST, GraphQL, JSON Schema, JSON:API
• CDNs (Fastly, Cloudflare)
• GitHub, BuildKite
• MySQL, Redis, Pulsar, Memcache
• Python, Django, FastAPI, Go, Gin, React, RabbitMQ, Celery, MySQL, DynamoDB, Cassandra, Redis
• DeepL, Smartling, Stripe
• Amazon Web Services (EC2, RDS, Aurora, AWS Translate, etc.), Terraform, Kubernetes, Splunk, Chronosphere, Cortex, DX, and other modern DevOps tools
• Bedrock, Claude, Cursor, LangChain, OpenAI, Gemini

Klaviyo is committed to a policy of equal opportunity and non‑discrimination. We do not discriminate on the basis of race, ethnicity, citizenship, national origin, color, religion or religious creed, age, sex (including pregnancy), gender identity, sexual orientation, physical or mental disability, veteran or active military status, marital status, criminal record, genetics, retaliation, sexual harassment or any other characteristic protected by applicable law.