Number and DateTime Formatting does not work for an fallbackLocale Array with multiple entries

[JoCa96]

vue & vue-i18n version

2.6.11, 8.17.3

Reproduction Link

https://codesandbox.io/s/number-and-datetime-formatting-does-not-work-for-an-fallbacklocale-array-with-multiple-entries-8g6nq

Steps to reproduce

1. Setup vue & vue-i18n
2. In the vue-i18n config provide numberFormats and dateTimeFormats for a language code
3. In the vue-i18n config provide an array for fallbackLocale, where a language code is the one for which you defined numberFormats and dateTimeFormats
4. Make sure that the fallbackLocale array does have multiple entries and the default locale does not have any formats defined
5. In your template use $d and $n with a format that is only available for a language code of the fallbackLocal array
6. When running the app, check the console logs

What is Expected?

The dates and numbers should be rendered using the available numberFormats and dateTimeFormats for the fallback locale in the fallbackLocale array

What is actually happening?

Nothing is rendered. Instead the console logs the following warnings:
[vue-i18n] Fall back to 'en-us,de' datetime formats from 'en-uk' datetime formats.
[vue-i18n] Fall back to 'en-us,de' number formats from 'en-uk' number formats.