Cortana is available in these regions for these languages:
China: Chinese (Simplified)
United Kingdom: English
United States: English
Your PC needs to have one of these video cards: AMD: AMD Radeon HD 7000 series, HD 7000M series, HD 8000 series, HD 8000M series, R9 series and R7 series. NVIDIA: GeForce 600 series or later, GeForce 800M series or later, Quadro Kxxx series or later.
Go to Settings > Time & language > Region & language.
Select Add a language.
Select the language you want to use from the list, then choose which region’s version you want to use. Your download will begin immediately.