Brilleglassene har antirefleksbehandlingen og hærdningen.

Because brilleglassene is a definite plural form: the lenses.

With many Danish nouns, definiteness is shown by adding an ending to the noun itself.

For brilleglas, the pattern is:

• et brilleglas = a lens
• brilleglasset = the lens
• brilleglas = lenses
• brilleglassene = the lenses

So -ene here is doing the job that English the does with a plural noun.

The base word is brilleglas, and when certain endings are added in Danish, the s is often doubled in writing:

• glas
• glasset
• glassene

The compound brilleglas follows the same pattern:

• brilleglasset
• brilleglassene

So the extra s is part of normal Danish spelling, not a separate meaning.

That is one of the big differences between English and Danish. Danish usually expresses the by adding it to the noun.

For example:

• behandling = treatment
• behandlingen = the treatment
• hærdning = hardening
• hærdningen = the hardening

So in this sentence, Danish is not missing the. It is built into the noun forms.

Yes, antirefleksbehandling og hærdning would also be possible, and in many product-description contexts it may sound more natural.

The definite forms:

• antirefleksbehandlingen
• hærdningen

can sound like specific treatments that are already known from the context.

In a more general feature-list style, Danish often prefers the bare nouns:

• Brilleglassene har antirefleksbehandling og hærdning.

So the given sentence is understandable, but the definite forms may sound a little more specific than English learners expect.

Har is the present tense of at have.

It works much like English has/have when talking about features, properties, or what something comes with.

So the structure is simply:

• Brilleglassene = subject
• har = has/have
• antirefleksbehandlingen og hærdningen = what the lenses have

This sentence has the normal main-clause word order:

• Brilleglassene = subject
• har = finite verb
• antirefleksbehandlingen og hærdningen = object/complement

So in this case, the order looks very similar to English.

A useful bigger rule is that Danish is a verb-second language, which means the finite verb normally stays in second position in main clauses.

Yes. Danish writes compounds as one word, much more often than English does.

For example:

• brilleglas = brille
  • glas
• antirefleksbehandling = anti
  • refleks
    • behandling

Then Danish adds the definite ending afterward:

• antirefleksbehandling → antirefleksbehandlingen

A good strategy is to identify the last part of the compound, because that usually tells you the core meaning and the gender of the whole word.

In Danish compounds, the last element usually decides the gender.

So:

• et glas → et brilleglas
• en behandling → en antirefleksbehandling
• en hærdning

That is why the definite forms are:

• brilleglasset
• antirefleksbehandlingen
• hærdningen

This is a very useful rule when learning long Danish nouns.

A Dane would understand it, but a slightly more natural version in a product or sales context would often be:

• Brilleglassene har antirefleksbehandling og hærdning.

Another natural option is:

• Brilleglassene er antirefleksbehandlede og hærdede.

So the original sentence is not wrong in an obvious way, but it can sound a bit less idiomatic than the most natural Danish phrasing.