"It rained last week."

Translation: 上星期下了雨。

[brobinsoncrusoe]

Wouldn't 下雨了 also be correct?

[Handrisuselo]

Yes, I agree with you. "下雨" means "to rain" (as a verb).

下了雨 seems very odd

[Cinnamon5230]

Yes.

[111111169469]

No.
'Le' is used differently in different places.

There are many uses; but most popular are:

1. It is used directly after the verb to indicate a past event

2. It is used after a full sentence to indicate that some status has changed.

This case is the first one.
Since 'xia yu' is actually a mixture of xia(to pour; verb) and yu(rain; noun), le has to be directly after xia

[Gabrielle145359]

了 directly after the verb dors not indicate a past event. It indicates a completed action. It can be used to indicate the completion of future actions.

[Alan946894]

2020.7.10
Can you give us some examples where 了 is completing present and future events?

I mean I guess 我回来了。can be translated as "I'm home." and 你回来了 can be "You are back." which in English we would use the present tense

[e1VpVxkl]

上星期下雨了. (shàng xīng qī xià yǔ le.) = Accepted: 06 mrt. 2020

[Handrisuselo]

下了雨 seems very strange to me.

[llfoolj]

How long will it take for them to fix the audio from saying liao instead of le?

[duckmaestro]

Is '了' neccessary? Isn't it already clear it's the past?

[DirkJacob1]

Yes

[medjzL]

Having Le immediately after Xia is consistent with this lesson's indication of Xia as the main verb for both rain and snow

[ReubenMild]

It wasn't just now...

[OkuTain]

My translation should be correct

[OkuTain]

My answer was exactly the same as Duolingo's. Why it didn't give me correct

[richard711603]

A translation tool gave： '下了雨‘ - it rained '下雨了' - it is raining