Android pluralization looks simple until it isn’t. You add a <plurals> block, define one and other, and ship. Then you add a new language, QA finds broken grammar, or your build starts failing because the plural categories don’t match what that language actually needs. Android’s rules are ICU-based and language-specific, which means quantity="one" does not always mean “the number 1,” and many languages require categories like few, many, or two. Plural strings also almost always contain placeholders, and translation updates can quietly remove, reorder, or corrupt them—often without an obvious error until runtime. This guide explains how Android plurals really work, the most common mistakes teams make, how to structure plural resources defensively in your base language, and what to validate so plural bugs don’t show up late (or in production).