「５しゅうかん 日本語 を べんきょうしました」or 「日本語 を ５しゅうかん べんきょうしました」

Question

わたしは　くにで　５しゅうかん　日本語　を　べんきょうしました。

わたしは　くにで　日本語　を　５しゅうかん　べんきょうしました。

I have seen sentence in this two orders. Which is more appropriate?

Answer 1

From my personal experience,

I would say that it depends on the circumstance...
It's probably pretty rare in daily life that that much specific information would ever occur in one sentence.

Usually there would be more than enough context to be able to avoid saying

1. what you did （study Japanese）,
2. where you did it (in your home country) and
3. for how long (5 weeks) and then

4. emphasizing that it was you （わたしは）

   all in one utterance.

Here's an example of where it might happen though...

The teacher says:

[皆]{みな}さんバケーションをどのように[過]{す}ごしましたか？ボブは？
 - How did you all spend your vacations? How about you Bob?

Bob says:

あっ、えぇと．．．[九州]{きゅうしゅう}へ[行]{い}ってボランティアしました。
 - Ummm, I went to Kyushu and did some volunteer work. 

Then Sue says:

あたしは[香港]{ほんこん}で[買]{か}い[物]{もの}してた！[広東語]{かんとんご}もちょっと[勉強]{べんきょう}しました。
- I went shopping in Hong Kong! And I studied a little bit of Cantonese.

You might say:

[僕]{ぼく}は[故郷]{ふるさと}に[帰]{かえ}って日本語を３[週間]{しゅうかん}[勉強]{べんきょう}していました。

• I went back home and studied Japanese for 3 weeks.

OR

僕は[故郷]{ふるさと}に帰って３週間日本語を勉強していました。

• I went back home and for 3 weeks I studied Japanese .

This one sounds a little repetitive in English, just because we have to repeat "I"... Doesn't sound that way in Japanese.

OR

僕は３週間[故郷]{ふるさと}に帰って日本語を勉強していました。

• I went back home for 3 weeks and studied Japanese.

OR

３週間僕は[故郷]{ふるさと}に帰って日本語を勉強していました。

• For 3 weeks I went back home and studied Japanese.

This last one sounds like your over-emphasizing the fact that you were there for 3 whole weeks, so it would be a little out of place in this context.

Long story short, 3週間日本語を勉強しました and 日本語を3週間勉強しました, are grammatically equivalent.

Answer 2

Both are same, you can choose as you like.

Answer 3

They're pretty similar; no one would bat an eye if you swapped them most of the time. However there is a slight difference in that there's an implied emphasis or contrast on the beginning of a sentence. So you'd be more likely to use the first in talking about what you did at different times: For five weeks, I studied Japanese [and then...] vs. maybe using the second to contrast with a different language: I studied Japanese for five weeks [but my Spanish is better.]

Also, yeah, the sentences as you abbreviated then for your question title are much more conversational than the full text, but that's also not something you really need to worry about as a beginner.