Ni akceptos la takson, kondiĉe ke la kosto restu sama.

Because -os marks the future in Esperanto.

• akcepti = to accept
• akceptas = accept / am accepting / accepts
• akceptos = will accept

So Ni akceptos means we will accept, which matches a future decision or promise.

The -n is the accusative ending, which usually marks the direct object of the verb.

In this sentence:

• Ni = we
• akceptos = will accept
• la takson = the thing being accepted

So la takson is the direct object, and that is why it takes -n.

Without -n, the grammar would be incomplete.

Yes. kondiĉe ke is a standard expression meaning provided that, on condition that, or as long as.

You can think of it as introducing a condition:

• Ni akceptos la takson, kondiĉe ke...
  = We will accept the estimate, provided that...

It is very commonly followed by a verb in -u form, because the condition is not being stated as a simple fact.

Because after kondiĉe ke, Esperanto often uses the -u verb form to show a desired, required, or conditional situation.

So:

• restas = remains / is remaining
• restos = will remain
• restu = remain / should remain / be to remain

In this sentence, restu does not mean a command to the cost. It means something like:

• provided that the cost remain the same
• on condition that the cost stays the same

This use of -u is very natural in Esperanto after expressions of condition, purpose, wish, or requirement.

Not really, at least not in the ordinary imperative sense.

The -u ending covers several ideas in Esperanto, including:

• commands
• requests
• wishes
• intentions
• conditions
• requirements

Here it expresses a condition, not an order. No one is literally commanding the cost. The sentence means that acceptance depends on the cost staying unchanged.

Because sama is describing la kosto, not functioning as a direct object.

In la kosto restu sama:

• la kosto is the subject
• restu is the verb
• sama is a predicate adjective describing the subject

Predicate adjectives in Esperanto normally do not take -n just because the main sentence has an object somewhere else.

Compare:

• La kosto estas sama. = The cost is the same.
• La kosto restu sama. = The cost should/remain the same.

If you said saman, that would suggest an accusative role, which is not what is happening here.

Yes, but it would change the nuance.

• la kosto restu sama = provided that the cost remain the same / should remain the same
• la kosto restos sama = provided that the cost will remain the same

The version with restu sounds more idiomatic after kondiĉe ke, because it presents the clause as a condition rather than a plain statement about the future.

So restos may be understandable, but restu is the more standard choice here.

Because kondiĉe ke la kosto restu sama is a subordinate clause, and Esperanto often separates such clauses with a comma, especially when they come after the main clause.

Main clause:

• Ni akceptos la takson

Subordinate conditional clause:

• kondiĉe ke la kosto restu sama

The comma helps show the structure clearly. It is good standard punctuation here.

Yes. Esperanto word order is fairly flexible, as long as the grammar remains clear.

For example, you could also say:

• Kondiĉe ke la kosto restu sama, ni akceptos la takson.

This puts the condition first. The meaning stays the same, but the emphasis shifts slightly toward the condition.

Because Esperanto marks the object with -n, word order is often freer than in English.

No. Even though takso may look a bit like tax, it usually means estimate, evaluation, or assessment.

So la takson here is not necessarily a government tax. It is more likely something like:

• an estimate
• an appraisal
• an assessment

This is a good reminder that similar-looking words are not always true equivalents.