Add German translations for notifications

[bastiankistner]

What does this PR do?

Add German translations for notifications.

These changes will impact:

• [x] commenters
• [ ] moderators
• [ ] admins
• [ ] developers

What changes to the GraphQL/Database Schema does this PR introduce?

None

Does this PR introduce any new environment variables or feature flags?

No

If any indexes were added, were they added to INDEXES.md?

None

How do I test this PR?

• enable DSA in admin settings
• write a comment
• reject the comment
• check notifications

Were any tests migrated to React Testing Library?

No

How do we deploy this PR?

As usual

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