TYPO3 Core

In a multi-site multi-language installation the sites configuration is built from various imported files. If you import languages in a certain order they appear in the reversed order in the resulting configuration. This means that the wrong language is seen as the default language.

imports:
  - { resource: 'English.yaml' }
  - { resource: 'German.yaml' }

and English.yaml contains stuff like

languages:
  -
    title: English
    enabled: true
    languageId: 0
    base: '/'
    typo3Language: default
    locale: en_US.UTF-8
    iso-639-1: en
    navigationTitle: English
    hreflang: en-US
    direction: ''
    fallbackType: strict
    flag: gb

Then the German configuration comes first, which makes that the default configuration.