Yojana is the unit of measurement of distance. It was used anciently and even used by some very old people in villages.
Yes, it can be roughly translated as league in English language, but it's counting was not like a league, which originally meant the distance a person can walk in an hour.
In ancient times people in India used to measure things by the size of fingers. They would say, this stick is 5 anguli (fingers) long. I have even heard old people in the village using that measurement still today. Only after the rule of the Britishers that we adopted the metric system of measurement.
So one yojana was a unit of distance measurement whose smallest unit was one finger (few inches roughly). So the Artha Sashtra gives the definition of yojana as below:
1 yojana = 4 gorutas; 1 goruta = 1000 dhanus; 1 dhanu = 96 angulas. So
by taking one angula (finger) as ¾ inch, one yojana becomes about 4.54
statute miles. Which is roughly 5 miles (8 km).
But later on by comparing with other sources, the calculation becomes different. For example, Aryabhata mentions earth's diameter as 1050 yojana. And comparing it with the current value of 7928 miles we get 1 yojana as 7928/1050 = 7.55miles (around 12km).
So one yojana has varying interpretations in terms of kilometers. Anciently it was about 8km. But now generally it's converted between 13 to 16 km.
Please see this article, it has good information.
Vedic Cosmography and Astronomy