"They have learned Chinese for a long time."

Translation: 他们学中文学了很久了。

[Swazzer30]

他们中文学了很久了

is also correct...

[hesesols]

The 了 at the end may not be necessary

[wordgeek416]

The word list choices for this sentence are strange. The only way to enter the suggested answer "他们学中文学了很久了" involves picking the words 他们, 学, 中, 文学, 了, 很, 久, 了

[FonnyTejo]

我觉得在那个句子应该要有“已经”。他们学中文已经很久了。那个已经可以表达 “have + v3” 的。