في كل أسبوع أذهب إلى السوق مرتين.

Yes. في كل أسبوع is a time expression, and Arabic often allows time expressions to move around in the sentence.

This sentence begins with it to set the time frame first:

في كل أسبوع أذهب إلى السوق مرتين

But you could also say:

أذهب إلى السوق مرتين في كل أسبوع

Both are correct. Starting with the time phrase gives a slight sense of As for every week... or Each week....

في usually means in, and here the phrase في كل أسبوع is literally something like in every week.

In Arabic, time expressions are often introduced by في. However, in this kind of sentence, Arabic can also omit it:

كل أسبوع أذهب إلى السوق مرتين

That is also very natural and often sounds closer to English every week.

So:

• في كل أسبوع = in every week / every week
• كل أسبوع = every week

Both work, though كل أسبوع is often the simpler everyday pattern.

After كل, Arabic very often uses a singular noun to mean every/each.

So:

• كل أسبوع = every week / each week

If you use a plural, the meaning changes:

• كل الأسابيع = all the weeks

This is a very common Arabic pattern:

• كل يوم = every day
• كل شهر = every month
• كل سنة = every year

So the singular after كل is normal and expected here.

Because the verb itself already tells you the subject.

أذهب means I go. The أ at the beginning marks first person singular.

So Arabic does not need أنا here.

You could say:

أنا أذهب إلى السوق مرتين في كل أسبوع

but that usually adds emphasis, contrast, or a more explicit tone. In normal sentences, Arabic often leaves the subject pronoun out because the verb already contains that information.

أذهب is the imperfect form of the verb ذهب.

In Modern Standard Arabic, the imperfect can express several things depending on context, including:

• present: I go / I am going
• habitual action: I go regularly
• future, if supported by context or a future marker

In this sentence, because of في كل أسبوع and مرتين, the meaning is clearly habitual:

I go to the market twice every week.

So here أذهب is best understood as I go regularly.

Because the verb ذهب normally takes إلى when you say where someone goes.

So:

• أذهب إلى السوق = I go to the market

In Modern Standard Arabic, ذهب usually needs that preposition for the destination.

This is one of those patterns you simply learn together:

• ذهب إلى = went to
• يذهب إلى = goes to
• أذهب إلى = I go to

السوق means the market, while سوق means a market.

Using ال here makes the destination definite. That can mean:

• a specific market known from context, or
• a general familiar place, like the market as a normal destination

If you said:

أذهب إلى سوقٍ مرتين في كل أسبوع

that would mean something more like I go to a market twice every week or to some market.

So السوق is more natural if the speaker means a known or regular market.

Arabic usually expresses frequency with the noun مرة meaning time/occasion.

So:

• مرة = once / one time
• مرتين = twice / two times
• ثلاث مرات = three times
• أربع مرات = four times

So مرتين is the normal Arabic way to say twice.

Using اثنتين by itself would just mean two (feminine), not twice.

Because مرتين is the dual form of مرة, and in this sentence it is in the accusative case.

The dual endings are:

• -ان in the nominative
• -ين in the accusative and genitive

So:

• مرتان = two times, in nominative position
• مرتين = two times, in accusative/genitive position

Here it functions as an adverbial expression of frequency, so the accusative is used:

أذهب إلى السوق مرتين

That is why you get مرتين, not مرتان.

It tells you how many times the action happens. In English, we would call it an adverbial expression of frequency.

So the structure is roughly:

• أذهب = I go
• إلى السوق = to the market
• مرتين = twice

It is not the object of the verb. It is more like a frequency/count expression modifying the action.

In traditional Arabic grammar, this kind of word often appears in the accusative as an adverbial element.

Because that is a very natural place for an expression of frequency in Arabic.

Arabic often puts the basic action first and then adds details such as place, time, and frequency. So this order is very normal:

أذهب إلى السوق مرتين

You can sometimes change the order for style or emphasis, but the final position is clear and natural.

For example, these are also possible:

• أذهب مرتين إلى السوق في كل أسبوع
• أذهب إلى السوق مرتين في كل أسبوع

But the original sentence sounds straightforward and well-formed.

A fully vowelled version would be:

في كُلِّ أُسْبوعٍ أَذْهَبُ إلى السُّوقِ مَرَّتَيْنِ

This shows several grammatical points:

• في كُلِّ: كل is genitive after في
• أُسبوعٍ: genitive as the second part of the كل + noun structure
• أذهبُ: indicative/imperfect with final -u
• إلى السُّوقِ: السوق is genitive after إلى
• مرتينِ: dual accusative/genitive ending -ين

In normal unvowelled writing, these endings are usually not written.

No. The sentence is correct, but Arabic has several natural ways to express the same idea.

For example:

• أذهب إلى السوق مرتين في الأسبوع
• كل أسبوع أذهب إلى السوق مرتين
• أذهب إلى السوق مرتين كل أسبوع

These all express roughly the same meaning.

The original sentence is completely acceptable, but many learners will also often hear مرتين في الأسبوع as a very common way to say twice a week.