Terminology

Locale

That's your language, plus a bit of extra info. Not all languages are locales and vice versa. For example, French is one language but it usually comes marked as fr-CA and fr-FR. That's because something that applies in Canada (CA) might not apply in France (FR). The currency for example, so if you're software is aiming at Canada, you want CA$, not €.

Chinese usually comes as two locales but covering just the one language. Usually you'll get zh-TW and zh-HANS (or something like that). Both are for the language Mandarin but essentially (currency and suchlike aside) they cover the differences in the writing system: the long character forms used in Taiwan and Hong Kong (e.g. 中國) and the abbreviated forms (e.g. 中国) used in Mainland China. But both are pronounced zhōngguó.

Localization

Often abbreviated l10n (don't ask why), the first letter being an L. To you and me, translation. A new word was coined because when you translate software, it's not just translation. Other things get involved, like setting the right codes which tell the software what language its in, picking search engines which are right for your language, changes number settings (for example, does your language use a comma or dot as a separator between thousands: 1,000 or 1.000?). Stuff like that.