Die mondhigiëne is belangrik.

In Afrikaans, die is the normal definite article, so it often translates as the in English.

• die mondhigiëne = the oral hygiene / the mouth hygiene
• Afrikaans does not change the article for gender the way some languages do.
• The same die is used with many singular and plural nouns.

So in this sentence, Die mondhigiëne simply means The oral hygiene or more naturally Oral hygiene.

No. In Afrikaans, die is usually pronounced roughly like dee.

So:

• die ≈ dee

That is one of the first pronunciation differences English speakers notice.

Afrikaans often writes compound nouns as a single word, much like Dutch and German.

Here:

• mond = mouth
• higiëne = hygiene

So:

• mondhigiëne = mouth hygiene / oral hygiene

English often uses two words where Afrikaans prefers one compound word.

The ë shows that the vowels are pronounced separately, rather than blending into one sound.

In higiëne, it helps signal that the ending is pronounced in separate syllables. For a learner, the important point is:

• the dots are not optional in standard spelling
• they help guide pronunciation

So you should write higiëne, not higiene.

Afrikaans and English are both Germanic languages, so sometimes they have similar-looking words. Is is one of them.

In this sentence:

• is = is

That said, you should not assume identical words always behave exactly the same in every context. But here, the meaning and use are very close to English.

Because this is a normal Afrikaans main clause with the same basic word order as English:

• Subject + verb + complement
• Die mondhigiëne
  • is
    • belangrik

So:

• Die mondhigiëne = subject
• is = verb
• belangrik = adjective/complement

This is very similar to English Oral hygiene is important.

Not in this sentence. After is, the adjective stays in its basic form.

So:

• Die mondhigiëne is belangrik.
• Die boek is belangrik.
• Die reëls is belangrik.

In all of these, belangrik stays the same.

Afrikaans adjectives sometimes do change when they come before a noun, but after is they usually do not.

Yes, depending on the meaning you want.

• Die mondhigiëne is belangrik. = The oral hygiene is important / Oral hygiene is important
• Mondhigiëne is belangrik. = Oral hygiene is important

Without die, the statement sounds more general. With die, it can sound more definite or specific, though in practice Afrikaans sometimes uses the article where English would not.

It is correct and understandable, but in everyday speech people may also use more common or practical expressions depending on context, such as talking about:

• jou tande borsel = brushing your teeth
• tandversorging = dental care
• mondsorg = oral care

So mondhigiëne is a valid word, but it can sound a bit formal or medical depending on the situation.

A rough learner-friendly guide would be:

• Die ≈ dee
• mond ≈ mont or mond with a short o
• higiëne ≈ hee-ghee-YEH-nuh (roughly)
• is ≈ iss
• belangrik ≈ buh-LANG-rik or beh-LANG-rik (roughly)

So the whole sentence is approximately:

• dee mond-hee-ghee-YEH-nuh iss beh-LANG-rik

This is only an approximation, but it is a useful starting point.

Usually, in this meaning, it is used as an uncountable noun, like hygiene in English. So in most normal contexts, you would not use a plural.

You would normally say:

• Mondhigiëne is belangrik.

rather than trying to make it plural.

It is fairly neutral, but slightly formal because of the word mondhigiëne.

It would fit well in:

• health advice
• school material
• posters
• medical or dental contexts

In casual conversation, speakers might say something more everyday, but this sentence is perfectly natural and correct.