The language of TST. is different from Firefox or my OS setting. Both Firefox and OS use traditional chinese (zh-TW locale), but TST. use simplified chinese (zh-CN locale).
The language of context menu should be same as the Firefox or OS (zh-TW)
The language of context menu (and preference page) is zh-CN

TST's package includes both zh_CN and zh_TW (note that _ instead of -, it is a rule of WebExtensions) and there is no more codes around localization, so correct locale should be selected by Firefox itself. Hmm...
Does this problem happens only on TST? Do you know any other addon which have both zh_TW and zh_CN locales and zh_TW is correctly selected?
Yes, Stylus use zh_TW correctly.
Maybe the case is related? mozilla/activity-stream#2452
@cmOti
I've already made zh_TW locale, and accepted by author. But you need to wait next version (or just use dev version).
I think the problem is firefox will use zh_CN rather than en if an addon don't have zh_TW locale.
Oh, sorry, I forgot that it was added after 2.2.11 was released...
I installed the dev version and everything looks fine. Thank you!
Most helpful comment
Oh, sorry, I forgot that it was added after 2.2.11 was released...