Installation error on Platform.sh/Pantheon when using non-English

Problem/Motivation

When doing an installation on a fresh Pantheon or Platform.sh environment and selecting a language other than English, e.g. Spanish the installation can not be finished. Instead it throws an error with the message:
"Drupal is already installed".

Steps to reproduce:
- Create a new trial on Platform.sh with this link: https://accounts.platform.sh/platform/trial/opensocial/setup
- After environment is build, go to the URL.
- During installation select language "Dutch" and submit form.
- You should see error message "Drupal is already installed."

It most likely has something to do with folder creation during installation the first time. After the database is dropped it is possible to follow the installation the second time in any language.

Proposed resolution

There is no solution yet, we need to research. One option is to drop the database (either via Platform CLI or Terminus) and try again.

Remaining tasks

- Look into what might be causing this.
- Propose a solution.
- Test and review it.

Original report by [wtchan]

As reported on: https://github.com/lquessenberry/OpenSocialOnPantheon/issues/1