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"Mana aku ni takut" means something like "How can you suggest that I'm scared", or "What do you mean by saying that I'm scared". Actually, it's rather difficult to find an equivalent in English.
In fact, the more I think about it, the more I like "Where got I'm scared". It's simple and direct, and (with a bit of effort) I can understand it perfectly. I might even start using the construction myself.