Improve de-CH locale with new formats and content

[stefnnn]

Motivation / Background

The current Swiss German (de-CH) locale is quite outdated and many US defaults are used. There is no fallback to the "de" locale, which might be a consideration at some point.

Additional information

I reformatted the YAML file to conform to the dashed-single-line format.

Checklist

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug, refactor something, or add a feature.
• Tests and Rubocop are passing before submitting your proposed changes.

[psibi]

Thank you!