Kontrolu la saldon antaŭ la transakcio.

Because -u is the Esperanto verb ending for a command, request, or exhortation.

So:

• kontroli = to check
• kontrolu = check! / do check

In this sentence, Kontrolu la saldon means Check the balance.

For an English speaker, this is the closest equivalent to the imperative in English. Esperanto uses the same -u form for commands like:

• Venu! = Come!
• Atendu! = Wait!
• Legu ĝin. = Read it.

The -n on saldon marks the direct object.

Here, the thing being checked is the balance, so saldo gets -n:

• Kontrolu la saldon. = Check the balance.

This is one of the most important features of Esperanto grammar. The direct object usually takes -n.

Compare:

• La saldo estas ĝusta. = The balance is correct.
  Here saldo is the subject, so no -n.
• Mi kontrolas la saldon. = I check the balance.
  Here saldon is the object, so it takes -n.

Because antaŭ is a preposition, and after a preposition the noun normally does not take -n.

So:

• antaŭ la transakcio = before the transaction

That phrase tells us when the checking happens.

A native English speaker may wonder whether every noun needs -n, but no: the -n is mainly for direct objects, and sometimes for certain other uses. After an ordinary preposition like antaŭ, you usually leave it off.

Saldo means balance, especially in a financial or account-related sense.

So in this sentence, la saldo most naturally means something like:

• the account balance
• the remaining balance
• the current balance

This is a common word in banking, finance, and payment contexts.

Because Esperanto uses la for definite nouns, and both nouns here are being treated as specific:

• la saldon = the balance
• la transakcio = the transaction

Unlike English, Esperanto has only a definite article (la) and no separate word for a/an.

So:

• la saldo = the balance
• saldo = balance / a balance, depending on context

In this sentence, using la sounds natural because it refers to a particular balance and a particular transaction relevant to the situation.

Yes. Esperanto word order is fairly flexible because endings show the grammatical roles.

So these are both fine:

• Kontrolu la saldon antaŭ la transakcio.
• Antaŭ la transakcio, kontrolu la saldon.

Both mean essentially the same thing: Check the balance before the transaction.

The first version is a straightforward neutral order. The second puts more emphasis on the time phrase before the transaction.

By itself, kontrolu is just a normal command/request form. It is not automatically rude, but it can sound direct, just like English Check the balance.

If you want to sound more polite, you can add words like:

• Bonvolu kontroli la saldon antaŭ la transakcio. = Please check the balance before the transaction.
• Mi petas, kontrolu la saldon antaŭ la transakcio. = Please, check the balance before the transaction.

So the basic sentence is grammatically fine; politeness depends on context and wording.

Yes, but it would mean something slightly different.

• antaŭ la transakcio = before the transaction
  This names the specific event.
• antaŭe = beforehand / earlier / previously
  This is more general.

So:

• Kontrolu la saldon antaŭ la transakcio. = Check the balance before the transaction.
• Kontrolu la saldon antaŭe. = Check the balance beforehand.

The original sentence is more precise because it explicitly mentions the transaction.

A rough English-friendly pronunciation is:

• Kontrolu ≈ kon-TRO-lu
• la ≈ lah
• saldon ≈ SAL-don
• antaŭ ≈ AN-taŭ
• la ≈ lah
• transakcio ≈ tran-sak-TSI-o

A few useful pronunciation notes:

• c in Esperanto is always like ts
• j is like English y
• ŝ is like sh
• stress is normally on the second-to-last syllable

So the full sentence is approximately:

kon-TRO-lu la SAL-don AN-taŭ la tran-sak-TSI-o

Yes. Transakcio is a normal Esperanto word meaning transaction.

It is clearly related to the English word, which often makes it easy for English speakers to recognize. In finance, commerce, and banking contexts, it is completely natural.

So the sentence sounds like standard, practical Esperanto, especially in a banking or payment setting.