Sweeping i18n leaks with four parallel AI agents — from 300 candidates down to 60 real bugs
For any app past a certain size that’s gone bilingual, the question “how much hardcoded Japanese is still hiding in our repo?” never quite goes away. A naive grep for [ぁ-んァ-ヶ一-龯] returns thousands of hits, and the vast majority are inside translation tables, already-branched code, or comments. The real leaks are buried. For one cleanup pass we attacked this with four parallel AI investigation agents plus AST-based false-positive filtering. The result: ~300 candidates detected → ~60 real leaks → cleaned up across five rounds. This post walks through the flow and the most interesting bug it uncovered — paying English users had been getting Japanese email from the Stripe webhook …