dotnet/wpf · error · InvalidOperationException

SR.Format(SR.RequiresExplicitCulture, TargetProperty.Name)

Error message

SR.Format(SR.RequiresExplicitCulture, TargetProperty.Name)

What it means

BindingExpressionBase throws this InvalidOperationException when a binding that does not have an explicit ConverterCulture or Source/StringFormat-related culture set must format a value (string formatting or conversion) but the target property has no unambiguous culture. WPF refuses to guess a culture because the inherited CultureInfo (via FrameworkLanguage/FrameworkProperty attached property) can change after load, which would silently produce different formatted strings. The error names the target property so the developer knows which binding to fix.

Solutions

  1. Set ConverterCulture on the Binding, e.g. ConverterCulture='en-US'.
  2. Set the Language attribute (xml:lang) on the root element of the XAML document, e.g. Language='en-US'.
  3. Set FrameworkElement.LanguageProperty globally (FrameworkElement.LanguageProperty.OverrideMetadata) to a default culture.
  4. If the value need not be culture-formatted, use CultureInfo.InvariantCulture explicitly via ConverterCulture or a converter.

Example fix

<!-- before -->
<TextBlock Text="{Binding Price, StringFormat={}{0:C}}" />

<!-- after -->
<TextBlock Text="{Binding Price, StringFormat={}{0:C}, ConverterCulture=en-US}" />
Defensive patterns

Strategy: validation

Validate before calling

if (binding.ConverterCulture == null && textBlock.Language == null)
    throw new InvalidOperationException("Binding requires explicit ConverterCulture or Language");

Try / catch

try { ApplyBinding(); }
catch (InvalidOperationException ex) when (ex.Message.Contains("culture"))
{
    logger.Warn("Binding needs explicit culture", ex);
}

Prevention

When it happens

Trigger: A Binding with StringFormat or a converter that formats strings, where ConverterCulture is not specified, the binding's Mode involves a transfer that requires culture-sensitive formatting, and the CultureInfo lookup yields an empty/neutral culture (typically in a compiled-XAML/binding path where XmlLanguage is not set). Thrown from BindingExpressionBase.SetupDefaultValueConverter/culture resolution path at BindingExpressionBase.cs:1271.

Common situations: Migrating to .NET Framework 4.0+ where the culture-resolution rules became stricter; XAML StringFormat bindings without ConverterCulture; strings like dates/numbers formatted differently than expected and the binding instead throws at runtime; apps with Language attribute omitted on the root element.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/0e042dec6a143214. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Data/BindingExpressionBase.cs:1271

                // if that doesn't work, use target element's xml:lang property
                if (_culture == null)
                {
                    DependencyObject target = TargetElement;
                    if (target != null)
                    {
                        if (IsInTransfer && (TargetProperty == FrameworkElement.LanguageProperty))
                        {
                            // A binding for the Language property needs the value
                            // of the Language property.  This circularity is not
                            // supported (bug 1274874).
                            if (TraceData.IsEnabled)
                            {
                                TraceData.TraceAndNotify(TraceEventType.Critical, TraceData.RequiresExplicitCulture, this,
                                    traceParameters: new object[] { TargetProperty.Name, this });
                            }

                            throw new InvalidOperationException(SR.Format(SR.RequiresExplicitCulture, TargetProperty.Name));
                        }

                        // cache CultureInfo since requerying an inheritable property on every Transfer/Update can be quite expensive
                        // CultureInfo DP rarely changes once a XAML document is loaded.
                        // To be 100% correct, changes to the CultureInfo attached DP should be tracked
                        // and cause a re-evaluation of this binding.
                        _culture = ((XmlLanguage) target.GetValue(FrameworkElement.LanguageProperty)).GetSpecificCulture();
                    }
                }
            }
            return (CultureInfo)_culture;
        }

        /// <summary> Culture has changed.  Re-fetch the value with the new culture. </summary>
        internal void InvalidateCulture()
        {
            _culture = DefaultValueObject;
        }

View on GitHub (pinned to 81131a70a4)