While it is absolutely mandatory to engage in weight training exercises every week, the timing depends on your fitness level, workout routine and how many days you perform it.
If you have just started exercises, then strength training twice a week is enough for you. That’s because is taxing for the body, also you need to master the form to avoid injury and muscle strain. So, a small and simple session in the beginning with lightweight is a preferred option.
After three to four weeks, you might increase the frequency and weight gradually to target more muscles groups.