I changed the language on my iPhone, but some words are still in english.

If I change my iPhone's language to Chinese, French, German, etc, the names of the weekdays in the native Weather app are still in English. So, no matter which language I choose, I still see the English words, "Monday, Tuesday, Wednesday ..." etc.

Also, in the native Calendar app, the name of the months are also still in English.

Even in my lock screen, it shows the day and month in English.

Suggestions?