Wat die lekkasie betref, diagnoseer die tegnikus die probleem.

It means as for the leak, regarding the leak, or when it comes to the leak.

Literally, betref means concerns or pertains to, so the whole phrase is an idiomatic way of introducing a topic.

So:

• Wat die lekkasie betref = as far as the leak is concerned
• die lekkasie = the leak
• betref = concerns / pertains to

This kind of opening is quite common in more formal or neutral Afrikaans.

Not really, at least not in the normal English sense of what?

In this expression, wat ... betref works together as a fixed pattern meaning as for ..., regarding ..., or when it comes to ....

So in this sentence, it is better to learn wat ... betref as one unit, rather than trying to translate wat by itself as what.

This is because Afrikaans follows a verb-second pattern in main clauses.

The first position in the sentence is taken by the topic phrase:

• Wat die lekkasie betref

Because that whole phrase comes first, the finite verb must come second:

• diagnoseer

After that comes the subject:

• die tegnikus

So the structure is:

• Wat die lekkasie betref = fronted topic
• diagnoseer = verb in second position
• die tegnikus = subject
• die probleem = object

If you started with the subject, you would say:

• Die tegnikus diagnoseer die probleem.

But once you move Wat die lekkasie betref to the front, inversion happens:

• Wat die lekkasie betref, diagnoseer die tegnikus die probleem.

Yes, diagnoseer is present tense here, meaning diagnoses.

Afrikaans verbs do not change according to the subject the way English verbs do. So:

• ek diagnoseer = I diagnose
• jy diagnoseer = you diagnose
• hy/sy diagnoseer = he/she diagnoses
• ons diagnoseer = we diagnose

So diagnoseer stays the same regardless of who is doing the action.

Die tegnikus means the technician.

Breakdown:

• die = the
• tegnikus = technician

Afrikaans uses die as the definite article for all nouns, whether singular or plural, and regardless of gender.

Die probleem is the direct object of the verb diagnoseer.

It tells you what the technician is diagnosing:

• die tegnikus = the technician
• diagnoseer = diagnoses
• die probleem = the problem

So the core clause is:

• Die tegnikus diagnoseer die probleem.
• The technician diagnoses the problem.

The opening phrase Wat die lekkasie betref just adds the topic or area being discussed.

The comma separates the fronted topic phrase from the main clause.

So:

• Wat die lekkasie betref, = as for the leak,
• diagnoseer die tegnikus die probleem. = the technician diagnoses the problem.

The comma helps show that the sentence begins with a topical or introductory expression.

Yes, it sounds somewhat formal or neutral-formal.

Wat ... betref is a perfectly normal structure, but it is more typical of careful speech or writing than very casual conversation.

In more everyday language, someone might use simpler alternatives depending on context, such as:

• Oor die lekkasie diagnoseer die tegnikus die probleem.
• Met die lekkasie diagnoseer die tegnikus die probleem.

But Wat die lekkasie betref is natural and correct, especially in written or professional contexts.

Not if you want the same meaning.

Wat die lekkasie betref at the beginning means as for the leak / regarding the leak.

But if you place wat die lekkasie betref after die probleem, it may sound like a relative clause attached to die probleem, which changes the structure and can make the meaning unclear or different.

So if your goal is to say Regarding the leak, the technician diagnoses the problem, the given sentence is the better structure:

• Wat die lekkasie betref, diagnoseer die tegnikus die probleem.

Betref is a verb meaning concerns, relates to, or pertains to.

You can see it in other expressions too, for example:

• Dit betref my nie. = It does not concern me.
• Wat die koste betref, is dit duur. = As for the cost, it is expensive.

In your sentence, betref helps create the meaning with regard to or as far as ... is concerned.

Yes, very easily. This is a productive pattern in Afrikaans.

For example:

• Wat die prys betref, is dit aanvaarbaar.
  = As for the price, it is acceptable.

• Wat die weer betref, lyk dit sleg.
  = As for the weather, it looks bad.

• Wat die verslag betref, sal ek dit môre klaar maak.
  = As for the report, I will finish it tomorrow.

So once you learn Wat X betref, you can reuse it with many different topics.