Encodings. Time Zones. Accented Characters. Daylight savings time. Do these words make you feel dread and anxiety? Among programmers, these topics are notorious for being the source of subtle, tricky bugs. Yet knowledge in this area is vital. To make this topic fresh & exciting, I created i18n-puzzles.com, inspired by the famous Advent of Code. After all, which programmer can resist a good puzzle?

Each puzzle comes with its own story, each puzzle teaches something new. Find a treasure with a UTF-8 validator, fix a banking scam by parsing right-to-left text, upgrade a time zone database in Antarctica to support science.

In March 2025 I published a new puzzle every day. Over 300 programmers from around the world competed. Now it’s time to look back and analyze the code they wrote. What are the best solutions? Which tools and libraries make it a little easier?

During this talk, I will illustrate some advanced topics related to Time Zones and Unicode, using code examples in Java, JavaScript, and other programming languages.