The extension ships en-US and zh-CN resources, but only en-US was ever
selected: every other browser language fell through to fallbackLng
("zh-CN"), so users on en, en-GB, en-CN, en-AU, ja-JP, fr-FR saw Chinese.
Match on the BCP 47 language subtag and normalise it to a resource key:
en* -> en-US
zh-Hans* / zh-CN / zh-SG / zh -> zh-CN
zh-Hant* / zh-TW / zh-HK / zh-MO -> zh-TW
anything else -> unchanged (fallbackLng default: en-US)
Simplified vs Traditional is decided by the script subtag (Hans/Hant) when
present, then by the region subtag, since Chrome reports zh-CN / zh-TW
rather than script subtags. The zh-TW branch is written now so adding a
Traditional translation later needs no code change.
chrome.i18n.getUILanguage() is now preferred over navigator.language, which
is unreliable on the chrome-extension:// origin the popup runs on.
Adds a locale-resolution regression matrix (28 cases).
Closes#168
iAstro