How can i say stupid in german?
And also 'yes, no, neither and thank you'

Question

Answer

stupid: dumm
yes: ja
no: nein
thank you: Danke (or: Dankeschön, or: Vielen Dank)

A: Bist Du dumm?
B: Ja, ich bin zu dumm, um Dich zu verstehen.
A: Nein, das glaube ich nicht.
B: Vielen Dank für dieses Gespräch.

A: Are you stupid.
B: Yes, I am too stupid to understand what you say.
A: No, I don't believe so.
B: Thank you very much for this conversation.

Al, I wish you good luck for your attempts to have a conversation with these words...

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Well lydia, the word stupid isn't exactly positive, is it?

Al, dafür hör' ich oft das Wort blöd.

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neither: weder

Exp: Weder bin ich dumm, noch taub.
English: Neither am I dumb nor deaf.

Depending on the usage of the word "neither" you need different german translations.

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blöd ist bisschen negativ.. Du kannst auch Dummkopf als Nomen nutzen.

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Also, I often hear the word "blöd" in German films and on the streets to mean "stupid" also. But I believe this word is informal or colloquial.