dotnet/wpf · error · ArgumentException

SR.SpecificNumberCultureRequired

Error message

SR.SpecificNumberCultureRequired

What it means

NumberSubstitution.ThrowIfInvalidCultureOverride requires the CultureOverride to be a specific (non-neutral, non-invariant) CultureInfo; otherwise it throws ArgumentException(SR.SpecificNumberCultureRequired). CultureOverride must identify an exact culture like 'fr-FR', not 'fr' or the invariant culture.

Solutions

  1. Set CultureOverride to a specific culture with a region, e.g. new CultureInfo("fr-FR") instead of "fr"
  2. Validate before assigning: a culture is valid when it's non-null, not invariant, and not neutral (culture.IsNeutralCulture == false)
  3. If only a language code is available, expand it to a default specific culture (e.g. "en" -> "en-US")
  4. Catch ArgumentException around the property/constructor set and fall back to CultureSource-based resolution

Example fix

// before
numberSubstitution.CultureOverride = new CultureInfo("fr"); // neutral culture
// after
var culture = new CultureInfo("fr-FR"); // specific culture
numberSubstitution.CultureOverride = culture;
Defensive patterns

Strategy: validation

Validate before calling

if (culture == null || culture.Equals(CultureInfo.InvariantCulture) || culture.IsNeutralCulture)
    culture = CultureInfo.CreateSpecificCulture(culture?.Name ?? "en");

Type guard

bool IsValidCultureOverride(CultureInfo c) => c != null && !c.Equals(CultureInfo.InvariantCulture) && !c.IsNeutralCulture;

Try / catch

try { numberSubstitution.CultureOverride = culture; }
catch (ArgumentException ex) { log.Warn("CultureOverride must be specific, falling back", ex); numberSubstitution.CultureSource = NumberCultureSource.AsCulture; }

Prevention

When it happens

Trigger: Setting NumberSubstitution.CultureOverride to a neutral culture (e.g. new CultureInfo("fr")), CultureInfo.InvariantCulture, an empty culture, or passing such a culture to the NumberSubstitution constructor.

Common situations: Deriving the culture from a language code that only has two letters (e.g. 'en', 'de'); using Thread.CurrentThread.CurrentUICulture when it is neutral; config storing 'invariant' as the override; parsing locale strings that lost their region suffix.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/6ac3cbe5e77d77bf. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/textformatting/NumberSubstitution.cs:83

        /// </summary>
        [TypeConverter(typeof(System.Windows.CultureInfoIetfLanguageTagConverter))]
        public CultureInfo CultureOverride
        {
            get { return _cultureOverride; }
            set { _cultureOverride = ThrowIfInvalidCultureOverride(value); }
        }

        /// <summary>
        /// Helper function to throw an exception if invalid value is specified for
        /// CultureOverride property.
        /// </summary>
        /// <param name="culture">Culture to validate.</param>
        /// <returns>The value of the culture parameter.</returns>
        private static CultureInfo ThrowIfInvalidCultureOverride(CultureInfo culture)
        {
            if (!IsValidCultureOverride(culture))
            {
                throw new ArgumentException(SR.SpecificNumberCultureRequired);
            }
            return culture;
        }

        /// <summary>
        /// Determines whether the specific culture is a valid value for the 
        /// CultureOverride property.
        /// </summary>
        /// <param name="culture">Culture to validate.</param>
        /// <returns>Returns true if it's a valid CultureOverride, false if not.</returns>
        private static bool IsValidCultureOverride(CultureInfo culture)
        {
            // Null culture override is OK, but otherwise it must be a specific culture.
            return
                (culture == null) ||
                !(culture.IsNeutralCulture || culture.Equals(CultureInfo.InvariantCulture));
        }

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