https://github.com/bitcoin/bitcoin/blob/5180a86c96bc05d2a731f70f36aae28ab5a3fad4/src/qt/sendcoinsdialog.cpp#L339

I think this is %1, not %2
questionString.append("<hr /><span style='color:#aa0000;'>");
        questionString.append(BitcoinUnits::formatHtmlWithUnit(model->getOptionsModel()->getDisplayUnit(), txFee));
        questionString.append("</span> ");
        questionString.append(tr("added as transaction fee"));
        
        questionString.append(" (" + QString::number((double)currentTransaction.getTransactionSize() / 1000) + " kB)");
    }
    
    questionString.append("<hr />");
    CAmount totalAmount = currentTransaction.getTotalTransactionAmount() + txFee;
    QStringList alternativeUnits;
    for (BitcoinUnits::Unit u : BitcoinUnits::availableUnits())
    {
        if(u != model->getOptionsModel()->getDisplayUnit())
            alternativeUnits.append(BitcoinUnits::formatHtmlWithUnit(u, totalAmount));
    }
    questionString.append(tr("Total Amount %1")
        .arg(BitcoinUnits::formatHtmlWithUnit(model->getOptionsModel()->getDisplayUnit(), totalAmount)));
    questionString.append(QString("<span style='font-size:10pt;font-weight:normal;'><br />(=%2)</span>")
        .arg(alternativeUnits.join(" " + tr("or") + "<br />")));
    questionString.append("<hr /><span>");
    if (ui->optInRBF->isChecked()) {
        questionString.append(tr("You can increase the fee later (signals Replace-By-Fee, BIP-125)."));
    } else {
        questionString.append(tr("Not signalling Replace-By-Fee, BIP-125."));
    }
    questionString.append("</span>");
    SendConfirmationDialog confirmationDialog(tr("Confirm send coins"),
        questionString.arg(formatted.join("<br />")), SEND_CONFIRM_DELAY, this);