Slegs indien die argitek die bouplan aanpas, lees ons dit.

Yes. Slegs indien means only if.

• slegs = only
• indien = if

So Slegs indien die argitek die bouplan aanpas... means Only if the architect changes/adapts the building plan...

This is a fairly formal way to say it. In less formal Afrikaans, learners will also often see net as or just as, depending on the sentence.

Because indien introduces a subordinate clause, and in Afrikaans subordinate clauses usually send the finite verb to the end.

So:

• die argitek pas die bouplan aan = the architect adapts the building plan
  Here, in a main clause, the separable verb is split: pas ... aan.

But after indien:

• indien die argitek die bouplan aanpas
  The verb moves to the end and becomes one word: aanpas.

This is very common in Afrikaans and is one of the main word-order patterns learners need to get used to.

Yes. The verb is aanpas, and in main clauses it often appears split as pas ... aan.

Compare:

• Die argitek pas die bouplan aan.
  = The architect adapts the building plan.

• ... indien die argitek die bouplan aanpas.
  = ... if the architect adapts the building plan.

So a useful thing to remember is:

• main clause: often split
• subordinate clause: usually together at the end

Afrikaans main clauses normally follow a verb-second pattern. That means the finite verb usually comes in the second position.

In this sentence, the first element of the whole sentence is the fronted subordinate clause:

• Slegs indien die argitek die bouplan aanpas

After that, the main clause begins, and the verb must come next:

• lees ons dit

So the order is:

1. fronted clause
2. finite verb
3. subject
4. rest of the clause

That is why it is lees ons dit, not ons lees dit.

Dit means it, and here it refers back to die bouplan.

So:

• die bouplan = the building plan / blueprint
• dit = it

Afrikaans often uses dit just like English uses it to refer back to something already mentioned.

Because die is the definite article the in Afrikaans.

So:

• die argitek = the architect
• die bouplan = the building plan

Afrikaans uses die for singular and plural nouns, unlike English, which changes only sometimes in other parts of grammar. Here it simply means the both times.

Bouplan is a compound noun:

• bou = build / building
• plan = plan

Together, bouplan means something like:

• building plan
• building design
• blueprint

The exact English translation depends on context, but the basic idea is a plan for construction.

Often, yes.

In everyday Afrikaans, as is very commonly used for if:

• As die argitek die bouplan aanpas, lees ons dit.

That said:

• indien is a bit more formal or careful in tone
• as is more common in ordinary speech

Because this sentence also has slegs (only), slegs indien sounds quite natural in a formal or written style.

Often yes, depending on tone.

• slegs = more formal, more neutral in writing
• net = very common in everyday speech

So you may hear:

• Net as die argitek die bouplan aanpas, lees ons dit.

But slegs indien sounds more formal and precise. A learner should recognize both, but the sentence you were given has a slightly more formal register.

Yes, that is very possible.

Afrikaans often uses the present tense where English might use present or future, depending on context. So this sentence can mean something like:

• Only if the architect adapts the building plan do we read it
• or, in context, Only if the architect adapts the building plan will we read it

The exact time reference usually comes from context, not from a special future verb form in the sentence itself.

Because Afrikaans does not need it here.

English sometimes says:

• Only if the architect changes the building plan, then we read it

But in standard English, that then is often unnecessary or even awkward. Afrikaans is similar here: the conditional relationship is already clear from slegs indien, so no extra then is required.

The sentence is complete and natural without any added word.

Yes. You could also say:

• Ons lees dit slegs indien die argitek die bouplan aanpas.

This means the same thing.

The difference is mainly one of emphasis and sentence flow:

• Slegs indien die argitek die bouplan aanpas, lees ons dit.
  This strongly foregrounds the condition.

• Ons lees dit slegs indien die argitek die bouplan aanpas.
  This starts more directly with we read it and adds the condition afterward.

Both are grammatical.

Not quite. Slegs indien is more restrictive than plain if.

Compare:

• As die argitek die bouplan aanpas, lees ons dit.
  = If the architect adapts the building plan, we read it.

• Slegs indien die argitek die bouplan aanpas, lees ons dit.
  = Only if the architect adapts the building plan, we read it.

The second sentence implies that this is the one condition under which we read it. So slegs indien adds a stronger sense of limitation.