i18n: Improve German Translation #890

[fupgang]

Description

Improves German translation.

Addressed Issue

resolves #890

Additional Details

• replaces some Dutch terms, e.g. key validation.confirmed
• replaces some placeholders not yet translated, e.g. api_key_comment
• replaces some wrong translations, e.g. enabled or configuration
• replaces some unusual translations, e.g. "dashboard" was translated to "Amaturenbrett", while "Dashboard" is frequently used in other applications (for example Grafana)
• similar for consumer_key and consumer_secret, the English terms should be more familiar in IT
• unifies some expressions, e.g. translate "password" always to "Passwort" (was "Kennwort" sometimes)

Checklist

• I have read and understand the contributing guidelines
• [ ] This PR introduces new or alters existing behavior, and I have updated the documentation accordingly

[nscuro]

Thanks a lot!