I actually didn't mean the time it took for them to start contributing, I meant the time it would take for them to complete the same task. Someone who knows th

I actually didn't mean the time it took for them to start contributing, I meant the time it would take for them to complete the same task. Someone who knows the ins and outs of their language won't have to look up or learn new stuff as they go for example. This isn't even necessarily restricted to languages or frameworks, if you've done something similar to an assigned task, you would likely have already encountered certain pitfalls and know the best way to complete the task.