Language preselected by the installer is not available

Problem/Motivation

Installation starts with selecting a language. The language preselected by the installer is not available and results in an error message.

Steps to reproduce

For some reason for me the default is British English (I'm using Mac and Chrome in English). As a non-native english speaker I don't make assumptions which English is the default for Drupal. In the next step installation process reports an error that the suggested language English, British is not available.

Proposed resolution

1. Only available languages should be offered by default.
2. For unsupported languages: instead of reporting these at a later stage as errors, the first selection should provide information wether or not language is available. This could be added as an inline message below the language select, sothing in line with "The selected language does not have user interface translation available".

Remaining tasks

The availability of different languages should be checked earlier in order to fix this.

User interface changes

API changes

Data model changes

Release notes snippet