the reason why 
der Grund, warum 
il motivo per cui 
la raison pour laquelle 
la razón por la que the reason why 11 之所以 [-] zhī suǒ yǐ (its-reason) the reason why: 我~迟到, 是因 为堵车 (dǔchē). I was late because of the traffic. || 他~没有告诉你真相 (zhēnxiàng), 是因为怕伤害你. He didn’t tell you the truth because he was afraid to hurt you. '
Lý do tôi gọi cho bạn là hỏi ý kiến của bạn. 
The reason I'm calling you is to ask your advice.
Der Grund, warum ich dich anrufe, ist, deinen Rat zu fragen.
เหตุผลที่ฉันโทรหาคุณคือการขอคำแนะนำจากคุณ
我打电话给你的原因是问你的建议。