My favorite would be English, i am so glad i did not skip the English lessons as a kid. My English might not be the best but i can talk, write and understand English and it helped me with so much trough my life. Swedish is of course also an nice language.
My favorite "BANGLA",for which international language day is dedicated. It's a achievement of Bangladeshi ,they sacrifice salam ,barkat,rafiq,zobbar ,shofiur for this language.