The phrase "Long lanh đáy nước in trời Thành xây khói biếc, non phơi bóng vàng" appears to be in Vietnamese. It conveys a picturesque and serene scene in nature, and it can be roughly translated as:

"Sparkling at the water's depth in the sky, A city built, its smoke blue, mountains bask in golden hue."

This description evokes an image of a tranquil and idyllic landscape, with clear water, a distant city enveloped in blue-hued smoke, and sun-kissed mountains casting a golden glow over the surroundings.