Translation:For the past three months I was working in Germany.
Actually, 过 indicates something in the past. Unless otherwise stated it should probably be assumed that the speaker likely no longer works in Germany.
wrong logic. 过 indicates the past is one thing. can't indicate the past without 过 is another.
I've come here with the same problem. Unless the sentence states that the work in Germany is over (does it?), it needs to use present perfect continuous.
I think that the Chinese sentence is inconclusive on thst count. The speaker might still be working in Germany, or the speaker might have just returned home.
I'm a native speaker and I agree with you. Without further context, I'd guess that the speaker is no longer working in Germany, e.g. 过去三个月我在德国工作（，现在回国了）. If the speaker is still working in Germany, they should rephrase it like 最近三个月我一直在德国工作（，但打算明年回国）.
It's more correct in English usage to say "have been working" than "was working."
The meaning is different; one is not more correct than the other without context. "I have been working...(and still am)" v "I was working...(but have just returned to China)".
I am not a native speaker of English, but in the grammar lessons we learned that a "for", indicating a continuation, always necessitates a perfect tense
Not always (though we usually tell students that at first.) For+past simple indicates a finished time period (we can also use from x to y). For+present perfect means the action continues (we can also use since x). e.g. I lived in Moscow for one year (but now I live in Guangzhou.) I've lived in Guangzhou for two years (and I'm here now.)