1. Define the numeric contract before the control

Record the business meaning, column type, precision, permitted range, blank rule, negative-value rule and supported languages. For an expense amount, a sensible contract might be: currency column, two decimals, £0–£1,000,000, required, no negatives, en-GB and pt-PT.

2. Map each user to an approved input language

Language() returns the current user's language tag. Map it to the locales the app has actually been designed and tested to support. Do not accept arbitrary regional variants without a test route.

// App.OnStart or screen.OnVisible
Set(
    varInputLanguage,
    If(
        StartsWith(Language(), "pt"),
        "pt-PT",
        "en-GB"
    )
);

3. Configure the modern Number Input

Set the properties below on numNetAmount. A Portuguese user sees and enters a comma decimal; a UK user sees and enters a full stop. The output remains the numeric numNetAmount.Value.

// numNetAmount properties
ContentLanguage = varInputLanguage
Precision       = DecimalPrecision.'2'
Min             = 0
Max             = 1000000
Step            = 0.01
AccessibleLabel = "Net amount in pounds, to two decimal places"

Microsoft states that the control's OnChange fires when focus leaves the field or when a step button is used—not on every keystroke. Put save-time validation on the submit action as well as visual feedback on the control.

4. Make validation visible and accessible

Use the control's validation state and a nearby label. Avoid relying on border colour alone; give people a clear message that a screen reader can announce.

// numNetAmount.ValidationState
If(
    IsBlank(numNetAmount.Value) ||
    numNetAmount.Value < 0 ||
    numNetAmount.Value > 1000000,
    ValidationState.Error,
    ValidationState.None
)

// lblNetAmountError.Text
"Enter an amount from 0.00 to 1,000,000.00"

// lblNetAmountError.Visible
numNetAmount.ValidationState = ValidationState.Error

5. Save the numeric value, not the formatted string

Patch .Value into a numeric or currency column. Round at the agreed storage boundary, not repeatedly during intermediate calculations.

If(
    IsBlank(numNetAmount.Value) ||
    numNetAmount.Value < 0 ||
    numNetAmount.Value > 1000000,
    Notify(
        "Check the net amount before saving.",
        NotificationType.Error
    ),
    Patch(
        Expenses,
        Defaults(Expenses),
        {
            NetAmount: Round(numNetAmount.Value, 2),
            TaxAmount: Round(Coalesce(numTaxAmount.Value, 0), 2)
        }
    )
)

6. Separate calculation from display

Calculate with numbers. Use Coalesce when a genuinely optional numeric value should behave as zero, then apply Text only in a read-only label.

// Numeric calculation
With(
    {
        NetValue: Coalesce(numNetAmount.Value, 0),
        TaxValue: Coalesce(numTaxAmount.Value, 0)
    },
    NetValue + TaxValue
)

// Read-only label: fixed GBP, user's separators
Text(
    Coalesce(varTotalAmount, 0),
    "[$-en-GB]£#,##0.00",
    Language()
)

The format-language placeholder tells Power Fx how to interpret the format string; the third argument tells it how the result should appear for the user.

7. Run the locale and boundary test matrix

Test with accounts whose language settings actually follow each route. Confirm the value both before and after save, then compare the underlying data-source value with the displayed label.