Kontoret öppnar igen den tionde augusti.

Kontor means office. The ending -et makes it definite singular, so kontoret means the office.

This is very common in Swedish: instead of adding a separate word like the, Swedish often adds the definite ending to the noun itself.

• ett kontor = an office
• kontoret = the office

Swedish often uses the present tense for planned or scheduled future events, especially when there is a time expression in the sentence.

So Kontoret öppnar igen den tionde augusti literally looks like The office opens again the tenth of August, but in natural English it is often translated as The office will open again on August 10th or The office reopens on August 10th.

Igen means again.

So öppnar igen literally means opens again. In natural English, that often becomes reopens.

That means the office was closed before, and it will open once more.

This is a standard Swedish way to express dates:

den + ordinal number + month

So:

• den första januari = the first of January
• den tredje maj = the third of May
• den tionde augusti = the tenth of August

English often says on August 10th or on the tenth of August. Swedish uses the ordinal form in this kind of date expression.

Here, den is part of the date expression, not something that matches kontoret.

So even though kontor is a neuter noun and often goes with det, dates are conventionally said as:

• den första april
• den femte juni
• den tionde augusti

So den here does not depend on kontoret.

Because Swedish usually does not need a preposition before a specific date in a sentence like this.

English:

• on August 10th

Swedish:

• den tionde augusti

So Kontoret öppnar igen den tionde augusti is normal Swedish. Adding på here would usually sound wrong.

Tionde is an ordinal number: tenth.

It comes from tio = ten.

Compare:

• tio = ten
• tionde = tenth

Ordinals are the forms used for dates, rankings, and numbered positions.

A few examples:

• första = first
• andra = second
• tredje = third
• tionde = tenth

In Swedish, names of months and days of the week are normally written with a lowercase letter unless they begin a sentence.

So:

• augusti
• september
• måndag

This is different from English, where August would be capitalized.

Yes. That is often the most natural translation.

• öppnar igen = literally opens again
• natural English = reopens

So if the meaning has already been given to the learner as something like The office reopens on August 10th, that is a very good translation.

Yes, but the original sentence is very natural.

Kontoret öppnar igen den tionde augusti puts igen close to the verb, which clearly gives the idea of reopening.

You might also see other word orders in different contexts, but this version is straightforward and idiomatic for saying that the office will open again on that date.