Hulle dink ek is mal.

Here is the breakdown:

• Hulle = they
• dink = think
• ek = I
• is = am / is / are depending on the subject
• mal = crazy / mad

So the structure is basically:

• Hulle dink = They think
• ek is mal = I am crazy

The whole sentence is made up of a main clause plus a second clause.

Afrikaans often leaves out that, just like English often does.

So:

• Hulle dink ek is mal = They think I am crazy
• Hulle dink dat ek mal is = They think that I am crazy

Both are possible, but the version without dat is very natural and common.

Yes. That is completely correct.

There is an important word-order difference:

• Without dat: Hulle dink ek is mal
• With dat: Hulle dink dat ek mal is

After dat, Afrikaans normally sends the verb to the end of the clause, so ek is mal becomes ek mal is.

That is a very common pattern in Afrikaans subordinate clauses.

Because Afrikaans changes word order depending on the type of clause.

In a normal clause, the order is usually:

• subject + verb + rest
• ek is mal

But after a subordinating word like dat, the verb usually moves toward the end:

• dat ek mal is

So both patterns are normal:

• Hulle dink ek is mal
• Hulle dink dat ek mal is

The first one keeps normal clause order in the second part because there is no dat.

Because ek is the subject of the second clause.

In ek is mal, ek is the one who is something, so it must be the subject form.

Compare:

• ek = I
• my = me

So Afrikaans works like English here:

• They think I am crazy
  not
• They think me am crazy

In Afrikaans, the verb wees is much simpler than English to be in the present tense.

You use is with different subjects:

• ek is = I am
• jy is = you are
• hy is = he is
• ons is = we are
• hulle is = they are

So unlike English, Afrikaans does not change the present form the same way.

Here, mal means crazy, mad, or insane.

A useful warning: English mad can also mean angry, but Afrikaans mal usually does not mean angry.

So in this sentence, mal means something like:

• crazy
• nuts
• out of your mind

Depending on context, it can sound serious, playful, or exaggerated.

Yes, mal is an adjective here.

After forms of to be, Afrikaans uses an adjective just as English does:

• ek is mal = I am crazy
• sy is moeg = she is tired
• hulle is gelukkig = they are happy

So mal comes after is because it describes the subject ek.

In this sentence, hulle means they.

But hulle can also mean them in other contexts. Afrikaans often uses the same form where English distinguishes they and them.

Examples:

• Hulle dink... = They think...
• Ek sien hulle. = I see them.

So you have to understand the role from the sentence structure.

A rough English-style guide is:

• Hulle ≈ HULL-uh or HU-luh
• dink ≈ dink
• ek ≈ uck or a short eck
• is ≈ iss
• mal ≈ mahl

A rough full pronunciation could be:

HULL-uh dink uck iss mahl

The exact vowels depend on accent, but that guide is close enough for a learner to start with.

It is neutral and natural. It works well in normal spoken and written Afrikaans.

If you want a slightly more explicit version, especially in writing, you could say:

• Hulle dink dat ek mal is.

But Hulle dink ek is mal is very common and sounds perfectly normal.