fix(i18n): improve date formatting with IntlDateFormatter fallback

[mercury233]

Currently, the language identifier used for Simplified Chinese (简体中文) is zh_cn, which is a basically correct abbreviation. However, although IntlDateFormatter can accept zh_cn as a parameter, zh_cn is not included in the list returned by ResourceBundle::getLocales(''). As a result, the current implementation of formatDate cannot correctly recognize Simplified Chinese.

Therefore, we can first try to create the IntlDateFormatter using $lang, and if an error occurs, fallback to English.

Fix #943

[mercury233]

I suspect that more languages are affected by this issue. After the fix, I tested all the languages in the list; all of them display correctly and do not fall back, except for Japanese (which is fixed in #977).