Scale and Libra both mean Libra. What's the difference ...

Scale is scale. However, it is recommended to use Libra when referring to constellations, because Libra is specially used to refer to Libra.

Balance or balance can refer to Libra, because they have the meaning of scale, but they are not standardized and not commonly used. Moreover, balance and balance are both polysemous words, and there are many other meanings, which are easy to cause confusion.