I was watching this video, and a phrase that struck out to me was

我学习汉语已经十年了 (translated as "I have studied Chinese for ten years")

I never learned this pattern for describing duration of an action, though; here are the ways I might say that sentence:

1. 我学习汉语学习了十年了 (I have been studying Chinese for ten years)
2. 我学习了十年（的）汉语 (I studied Chinese for ten years)
3. 我学习汉语学习了十年 (I studied Chinese for ten years)
4. 我已经十年没学习汉语了 (I haven't studied Chinese in ten years)

None of the ways I learned is like what was used in the video, though. My guess is that it's a sort of topic-comment construction, like

topic: 我学习汉语 (me studying Chinese)

comment: 已经十年了 (it's already been ten years)

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I would love any clarification on this sentence pattern!