Problem: The client is copying content to translate pages from English to German and is concerned about whether this method is appropriate for Google indexing. Solution: If you're duplicating content without the need for translation, using the Translation Management's duplication feature is correct. This is necessary only if you want the default language content to be displayed with a translated permalink (e.g., creating a permalink like /en-about-us with German content).
If the pages need to be translated, you should send them through a translation job (choosing "Translate" instead of "Duplicate content"). You can then enable the redirect based on browser language by following this documentation: Automatic redirect based on browser language.
However, it's important to note that English content is typically displayed in Google's index because the redirect is done via JavaScript, which also redirects Google's bot since its User-Agent is configured in English. For more information on how browser language redirect affects Google indexing, you can read this documentation: How browser language redirect affects Google indexing.
