ICU validator errors and fixes

Missing `other` clause

Every plural, select, and selectordinal should include other as fallback. Add it even if you do not expect unknown values.

Invalid placeholder names

Use stable identifier names like count, userName, or total_price. Avoid spaces or punctuation in argument names.

Unbalanced braces

Check nested blocks carefully. If one branch misses a closing brace, parsing fails for the whole message.

Runtime format errors

Some messages parse but fail at format time if variable types are wrong. Confirm numbers are numbers and date/time values are valid date objects or compatible inputs.

Recommended debugging order

Validate in validator, test variations in online editor, then verify locale categories in plural rules and plural playground.