Falls wir die Wohnung nehmen, brauchen wir einen Nachmieter für unsere alte Wohnung, weil die Kündigungsfrist noch drei Monate beträgt.

Falls means if.

In this sentence, falls wir die Wohnung nehmen = if we take the apartment.

A common learner question is how falls differs from wenn:

• falls often sounds a little more like in case or if it should happen that
• wenn is the more common general word for if in many situations

So:

• Falls wir die Wohnung nehmen, ...
• Wenn wir die Wohnung nehmen, ...

Both are possible here. Falls can sound a bit more tentative or hypothetical.

Because falls introduces a subordinate clause, and in German, the conjugated verb usually goes to the end of a subordinate clause.

So the normal main-clause order would be:

• Wir nehmen die Wohnung.

But after falls, it becomes:

• Falls wir die Wohnung nehmen, ...

This is a very common pattern:

• wenn
  • subject + ... + verb
• weil
  • subject + ... + verb
• dass
  • subject + ... + verb
• obwohl
  • subject + ... + verb

So nehmen is at the end because falls triggers subordinate-clause word order.

German uses commas to separate clauses more consistently than English does.

In this sentence, there are three clauses:

1. Falls wir die Wohnung nehmen
2. brauchen wir einen Nachmieter für unsere alte Wohnung
3. weil die Kündigungsfrist noch drei Monate beträgt

So the commas mark the boundaries between those clauses:

• subordinate clause: Falls wir die Wohnung nehmen
• main clause: brauchen wir ...
• subordinate clause: weil die Kündigungsfrist ... beträgt

That is why the sentence has commas around the main clause.

Literally, yes, nehmen means to take. But in this context, die Wohnung nehmen means something like:

• to take the apartment
• to go for the apartment
• to decide to rent the apartment

So it is not about physically taking it. It means choosing it or agreeing to rent it.

This kind of use is common in spoken German. A more explicit version could be:

• die Wohnung mieten = to rent the apartment

But die Wohnung nehmen sounds natural and idiomatic.

Because brauchen takes a direct object in the accusative case, and Nachmieter is masculine.

The phrase is:

• wir brauchen einen Nachmieter

Here is the masculine indefinite article:

• nominative: ein Nachmieter
• accusative: einen Nachmieter

Since Nachmieter is the thing that is needed, it is the direct object, so German uses the accusative:

• Wir brauchen einen Nachmieter.

Nachmieter means replacement tenant or next tenant.

It is made from:

• nach- = after
• Mieter = tenant

So a Nachmieter is the person who rents the apartment after you.

This is a very useful housing word in German-speaking countries, because people often talk about finding a Nachmieter when they want to leave a rental before the official notice period is over.

Because für always takes the accusative case.

So:

• für unsere alte Wohnung = for our old apartment

The noun Wohnung is feminine, and in the accusative singular, feminine looks the same as the nominative:

• nominative: unsere alte Wohnung
• accusative: unsere alte Wohnung

So nothing visibly changes in the noun phrase, but it is still accusative because of für.

A learner often expects a visible change, but with feminine singular here, the form happens to stay the same.

This is about adjective endings after a possessive word.

In unsere alte Wohnung:

• unsere = our
• alte = old
• Wohnung = apartment

Because Wohnung is feminine singular, the pattern is:

• unsere alte Wohnung

You can think of it as the normal feminine singular form in this type of noun phrase.

Compare:

• unsere alte Wohnung = feminine singular
• unser alter Mietvertrag = masculine singular
• unser altes Haus = neuter singular
• unsere alten Möbel = plural

So alte is the correct adjective ending for feminine singular after unsere.

Kündigungsfrist means notice period, especially in a contract such as a rental agreement or job contract.

It is a compound noun:

• Kündigung = cancellation, termination, notice
• Frist = deadline, period, time limit

So Kündigungsfrist is the period of time you must give in advance before ending the contract.

In this sentence:

• die Kündigungsfrist noch drei Monate beträgt

means that the required notice period is still three months.

Because weil introduces a subordinate clause, and in subordinate clauses, the conjugated verb goes to the end.

So:

• main clause: Die Kündigungsfrist beträgt noch drei Monate.
• subordinate clause: weil die Kündigungsfrist noch drei Monate beträgt

This is the same rule as with falls earlier in the sentence.

A useful pattern to remember:

• weil
  • subject + other elements + verb

Example:

• weil er keine Zeit hat
• weil das zu teuer ist
• weil die Kündigungsfrist noch drei Monate beträgt

Betragen means to amount to.

So:

• Die Kündigungsfrist beträgt drei Monate. = The notice period amounts to three months = more naturally in English, The notice period is three months

German often uses betragen with amounts, lengths, costs, distances, and periods of time.

Examples:

• Die Miete beträgt 900 Euro.
• Die Wartezeit beträgt zwei Stunden.
• Die Strecke beträgt 15 Kilometer.

You may also hear ist in some contexts, but beträgt is especially natural when stating an exact amount or duration.

Here noch means something like still.

So:

• die Kündigungsfrist beträgt noch drei Monate

means:

• the notice period is still three months
• or more naturally: there are still three months left in the notice period

Noch adds the idea that the period has not ended yet.

Compare:

• Die Kündigungsfrist beträgt drei Monate.
  = the notice period is three months
• Die Kündigungsfrist beträgt noch drei Monate.
  = there are still three months remaining / it is still three months

So noch gives extra information about the remaining time.

Because the sentence begins with a subordinate clause:

• Falls wir die Wohnung nehmen, ...

When a subordinate clause comes first, it takes the first position in the sentence as a whole. In a German main clause, the conjugated verb must then come second.

So the structure is:

• Falls wir die Wohnung nehmen, brauchen wir ...

Not:

• Falls wir die Wohnung nehmen, wir brauchen ...

This is the normal verb-second rule in German main clauses.

You can compare:

• Wir brauchen einen Nachmieter.
• Dann brauchen wir einen Nachmieter.
• Falls wir die Wohnung nehmen, brauchen wir einen Nachmieter.

In all three, the conjugated verb is in second position in the main clause.

Yes, both are possible, though the tone changes slightly.

• Falls → more tentative, if / in case
• Wenn → general if

And:

• weil = because
• da = also because / since, often a bit more formal or written

So these are possible alternatives:

• Wenn wir die Wohnung nehmen, brauchen wir einen Nachmieter ..., weil ...
• Falls wir die Wohnung nehmen, brauchen wir einen Nachmieter ..., da ...

The original sentence is very natural as it stands.

Not necessarily. Here unsere alte Wohnung usually means our old apartment in the sense of our previous/current apartment that we are leaving, not necessarily an apartment that is old in age.

German alt can work like English old in the sense of:

• former
• previous
• the one we had before

So in this sentence, it most likely means:

• our current apartment that we would be moving out of

not

• an apartment in an old building

Context tells you which meaning is intended.

Yes, that is a very natural translation in context.

Literally, the German says:

• we need a replacement tenant

But in real English, you would often say:

• we need to find a replacement tenant

The verb finden is not actually in the German sentence, but English often adds it because that is what the situation implies.

So both of these capture the meaning well:

• we need a replacement tenant
• we need to find a replacement tenant

The second is just a bit more explicit.