The question is flawed.
- If you want a successful career in USA, you need to know fluent English
- If you want a successful career in China, you need to know fluent fluent Mandarin (Chinese is not a language, same way as Indian is no language)
In exactly the same way, if you want a successful career in Germany (or any European country for that matter), then you need to know the language at fluent level.
So, the answer is - Learn German as much as you can. Its an investment that will benefit you, in career and life in Germany.
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