Jeg skriver kontrolcifrene og udløbsdatoen.

Because Danish usually puts the definite article on the end of the noun instead of using a separate word before it.

• udløbsdato = expiration date

• udløbsdatoen = the expiration date

• kontrolcifre = check digits
• kontrolcifrene = the check digits

So the sentence already includes the inside those noun forms.

They are different because one noun is plural definite and the other is singular definite.

• kontrolcifrene = the check digits
  
  • plural definite ending: -ne
• udløbsdatoen = the expiration date
  
  • singular definite ending: -en

So the endings show both number and definiteness.

The base singular form is et kontrolciffer.

Its forms are:

• et kontrolciffer = a check digit
• kontrolcifre = check digits
• kontrolcifrene = the check digits

This is a good example of how Danish nouns change form depending on singular/plural and definite/indefinite.

The base singular form is en udløbsdato.

Its common forms are:

• en udløbsdato = an expiration date
• udløbsdatoen = the expiration date
• udløbsdatoer = expiration dates
• udløbsdatoerne = the expiration dates

So in your sentence, udløbsdatoen is singular and definite.

skriver is the present tense form of the verb at skrive.

• at skrive = to write
• jeg skriver = I write / I am writing

In Danish, the present tense often ends in -r.
So after jeg, you use skriver, not the infinitive skrive.

It can mean either, depending on context.

Danish often uses the simple present where English might use either:

• I write
• I am writing

So jeg skriver kontrolcifrene og udløbsdatoen could mean either of those in English, depending on the situation.

Yes. This is the standard word order for a simple main clause:

• Jeg = subject
• skriver = verb
• kontrolcifrene og udløbsdatoen = object

So it follows the common pattern:

Subject + Verb + Object

That makes this sentence very straightforward.

Because Danish uses compound nouns very often, just like German does.

• kontrol
  • ciffer → kontrolciffer
• udløb
  • dato → udløbsdato

English often writes similar ideas as separate words, but Danish usually joins them into one word. This is very normal and important to get used to.

That s is a linking element often used in Danish compound nouns.

• udløb = expiry, expiration
• dato = date
• together: udløbsdato

The s helps connect the two parts. It does not always appear in compounds, but it is common in many words. You usually have to learn compound forms as vocabulary items.

og means and. It joins the two objects:

• kontrolcifrene
• udløbsdatoen

So the sentence says that both things are being written.

Not in this sentence as it stands. Normally, when a noun stands alone, Danish uses the ending-based definite form:

• udløbsdatoen
• kontrolcifrene

A separate article such as den, det, or de is usually used when there is an adjective before the noun:

• den nye udløbsdato = the new expiration date
• de sidste kontrolcifre = the last check digits

So without an adjective, the forms in your sentence are the natural ones.

In careful explanation, learners are often told it is something like yai or yigh, but in real speech it is usually much shorter and weaker.

A rough guide:

• jeg often sounds a bit like yai
• in fast speech, it can sound even more reduced

The exact sound varies by speaker and region, so the most helpful thing is to listen to native audio and repeat it rather than rely too much on English spelling.

It is neutral and natural. Nothing in it is especially formal or especially casual.

It would fit many ordinary situations, especially instructions, forms, customer service, or everyday explanations.