What is the monetary threshold (nisab) that makes Zakat obligatory, and can it be calculated using international currencies instead of gold?

"Determining the nisab (threshold for zakat) using paper currencies is neither wise nor Shariah-compliant due to their fluctuating value and susceptibility to economic changes in different countries. This is because paper currencies stand in place of gold and silver, for which the Shariah has set a specific nisab. What the questioner mentioned about the rising prices of gold also applies to paper currencies. There are fatwas on the website regarding the determination of nisab for zakat in paper currencies."