Jag köper ny tandkräm och en ny tandborste i affären efter jobbet.

Because Swedish often leaves out the article when talking about an uncountable substance, but uses an article with a countable singular noun.

• tandkräm = toothpaste, which is usually treated as an uncountable mass noun
• tandborste = toothbrush, which is a single countable object

So:

• ny tandkräm = new toothpaste
• en ny tandborste = a new toothbrush

This is similar to English: you can say I’m buying new toothpaste, but you normally say a new toothbrush.

Ny means new.

It appears twice because it describes two different nouns:

• ny tandkräm
• en ny tandborste

In Swedish, just like in English, the adjective usually has to be stated with each noun if both are being described separately. So you do not normally say one ny and let it automatically cover both items in this sentence.

Because tandkräm is usually treated as a non-count noun, like toothpaste in English.

You normally buy some toothpaste, not a toothpaste. Swedish works similarly here:

• Jag köper tandkräm = I’m buying toothpaste
• Jag köper ny tandkräm = I’m buying new toothpaste

If you wanted to talk about a specific unit, such as a tube, you would use a countable noun:

• en tub tandkräm = a tube of toothpaste

It is an en-word: en tandkräm.

You can tell that the adjective form ny fits an en-word singular noun. If it were an ett-word, you would expect nytt instead.

Compare:

• en ny tandborste
• en ny tandkräm
• ett nytt jobb

So the sentence gives you a clue about noun gender through the adjective form.

I affären means in the shop/store.

Swedish often uses i where English might use in or sometimes just say at depending on context. Here, i affären is the normal way to say that the buying happens in the store.

Also, affären is the definite form:

• en affär = a shop/store
• affären = the shop/store

So literally, this part is in the store.

Swedish often uses the definite form in places where English might sound more general.

Here, i affären is a very natural phrase for at/in the store. It does not necessarily mean one very specific store that has already been mentioned. In everyday Swedish, the definite form is often used in this kind of context.

So even if English might feel more general, Swedish still prefers:

• i affären not usually
• i en affär

The version with en affär would mean more literally in a shop, which is possible, but it is less natural in this everyday sentence.

Literally, efter jobbet means after the job, but in natural English it is usually translated as after work.

Jobbet is the definite form of jobb:

• ett jobb = a job
• jobbet = the job

Swedish often uses the definite form in fixed everyday expressions like this. So efter jobbet is the normal way to say after work / after finishing work.

A close parallel is how languages sometimes use a form that sounds more specific literally than it does in real usage.

It can mean either, depending on context.

Swedish present tense often covers both:

• I buy
• I am buying

So Jag köper ny tandkräm... could mean:

• a general present: I buy new toothpaste...
• a current action: I’m buying new toothpaste...
• sometimes even a planned near future, depending on context

Without extra context, English has to choose one, but Swedish does not always make that distinction.

Yes, it could be changed. Swedish is fairly flexible with adverbial phrases like these.

This sentence puts the place first and the time phrase after it:

• i affären = place
• efter jobbet = time

That is completely natural. But Swedish could also say:

• Jag köper ny tandkräm och en ny tandborste efter jobbet i affären.

That is grammatically possible, though the original version sounds smoother and more natural to many speakers.

If you start the sentence with Efter jobbet, then Swedish uses normal V2 word order:

• Efter jobbet köper jag ny tandkräm och en ny tandborste i affären.

Notice that köper comes before jag because the first position is already occupied by Efter jobbet.

Yes. Swedish very often forms compound nouns by writing them as one word.

Here:

• tand = tooth
• kräm = cream
• borste = brush

So:

• tandkräm = toothpaste
• tandborste = toothbrush

This is extremely common in Swedish. Where English may use two words or a closed compound depending on the word, Swedish usually writes these combinations as a single word.

Usually it means new toothpaste in the everyday sense: toothpaste you are buying because you need more, or perhaps a new kind/brand.

Like English new, Swedish ny can mean different things depending on context:

• newly bought
• different from the old one
• recently introduced
• newly made

In this sentence, the most natural interpretation is simply that the speaker is getting toothpaste and a toothbrush that are new to them, not necessarily freshly manufactured.

Yes. That would slightly change the feel.

• Jag köper... can mean I’m buying... or I buy...
• Jag ska köpa... means I’m going to buy...

So if the action is planned but not happening yet, Jag ska köpa ny tandkräm och en ny tandborste i affären efter jobbet may be clearer.

The original sentence is still very natural, especially if the context already makes the timing obvious.