Four Canvas Text Rendering Bugs That Only Appear in Spanish, French, and Portuguese

A developer maintaining multilingual web tools for generating PNG certificates and badges identified four recurring Canvas 2D text rendering failures that go undetected when testing only English and Japanese. French and Portuguese text runs 1.4–1.7 times longer than Japanese, while Spanish can expand to nearly three times the length, causing overflow and ellipsis that cuts off semantically critical words. A word-wrapping fix using a Latin character-class tokenizer introduced a new bug where accented characters like ç, é, and ã caused mid-word splits in Spanish, French, and Portuguese output. A mismatch between the DOM preview and the final PNG also emerged when auto-fit font sizing was applied only to the canvas render, breaking the tool's core promise of downloading exactly what the user sees. The developer recommends generating actual PNGs across all target locales as the only reliable detection method, since string-comparison tests cannot catch rendering-level failures.