Nummerflytningen tager en dag.

Because Danish, like English, often makes compound nouns by joining words together. Here:

• nummer = number
• flytning = moving / transfer

So nummerflytning means something like number transfer or number porting.

In Danish, these compounds are normally written as one word, not as separate words.

The -en is the definite article added to the noun, like the in English.

So:

• nummerflytning = number transfer / number porting
• nummerflytningen = the number transfer / the porting

A key difference from English is that Danish often puts the at the end of the noun instead of using a separate word.

Because this is a compound noun, the definite ending is added to the whole compound:

• nummerflytning → nummerflytningen

Tager is the present tense of tage, which usually means to take.

In this sentence, tage is used the same way as in English time expressions:

• Det tager en time = It takes an hour
• Nummerflytningen tager en dag = The number transfer takes a day

So tager simply means takes here.

Danish often uses the present tense for:

• general facts
• scheduled events
• near-future situations

So Nummerflytningen tager en dag does not have to mean only something happening right now. It can also mean:

• The number transfer takes one day
• The number transfer will take one day

This is very normal in Danish.

Because dag is a common gender noun in Danish, and common gender nouns use en in the indefinite singular.

So:

• en dag = a day

If it were a neuter noun, it would use et instead.

Because en dag means a day, an indefinite amount of time.

The sentence is giving a duration, not referring to one specific known day.

Compare:

• en dag = a day
• dagen = the day

Here, the meaning is about length of time, so en dag is the natural choice.

Not always exactly to the minute. In a sentence like this, en dag usually means about one day or within one day, depending on context.

For example, in customer-service or telecom language, it often means the process normally takes one day under normal conditions.

So it is usually understood as a practical time estimate, not necessarily a precise 24-hour measurement.

You could, but it changes the feel.

• Nummerflytningen tager en dag = The number transfer takes a day
  This usually refers to a specific transfer already being discussed.

• Nummerflytning tager en dag = Number transfer takes a day
  This sounds more general, like talking about the process as a concept, and can feel less natural in an ordinary sentence.

So the version with -en is very natural if the speaker means the specific transfer in question.

No, this is a very basic Danish sentence pattern:

• Nummerflytningen = subject
• tager = verb
• en dag = object / time expression

So it follows the normal order:

subject + verb + complement

That makes it very similar to English:

The number transfer takes a day.

Yes, but then the meaning changes slightly in emphasis, and the word order must follow Danish word-order rules.

For example:

• Nummerflytningen tager en dag.
• En dag tager nummerflytningen.

The second version is grammatical but sounds marked or unusual in everyday speech. Danish often uses verb-second word order, so when something other than the subject comes first, the verb still stays in second position.

In normal, neutral speech, Nummerflytningen tager en dag is the most natural version.