How One Dev Fixed Months of Wrong-Language Emails Using Stripe's Currency Field

A SaaS product unknowingly sent Japanese-language emails to English-speaking overseas customers for months after all four Stripe-triggered email types were hardcoded to Japanese. The development team evaluated three approaches to fix the language detection issue inside Stripe webhooks, including storing a language column in the database, querying the Stripe API, or inferring language from the currency field already present in the webhook payload. They chose currency-based inference because it requires no database migration, no extra API calls, and automatically applies the correct language to both new and existing users. A simple helper function maps USD to English and defaults all other currencies to Japanese, with room to expand for EUR or GBP markets later. The team also encountered a subtle PHP mb_language configuration trap during implementation that nearly undermined the fix.