Add Chinese

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Add translations for Simplified Chinese and Traditional Chinese.

From README.md

When creating a new language file ensure it follows the ISO 639 2-letter standard

Since scripts for both Simplified Chinese and Traditional Chinese share the same ISO 639 2-letter standard code (zh), I've provisionally named them as hans.json for Simplified Chinese and hant.json for Traditional Chinese in order to distinguish between them.

A better way to name these files can be discussed.

See also How should the language codes be formatted? from i18next FAQ