dotnet/runtime · critical · Error

invariant globalization mode is inactive and no ICU data…

Error message

invariant globalization mode is inactive and no ICU data archives are available

What it means

Thrown by init_globalization in loader/icu.ts when globalizationMode is set to Custom, All, or Sharded but getIcuResourceName returned no preferred ICU asset (no ICU files present in resources.icu). The user explicitly requested a non-invariant, non-shipped-fallback ICU mode but provided no ICU data, so the loader cannot proceed. Invariant mode would be the fallback, but the explicit mode forbids it.

Solutions

1. Ship the matching ICU archive(s): full (icudt.dat) for All, the EFIGS/CJK/no_CJK shard for Sharded, or your custom archive for Custom.
2. If you do not need locale-aware globalization, set globalizationMode = Invariant (or omit the config and let the loader fall back).
3. Verify the resources.icu array is populated and the asset names resolve.

Example fix

// before: Sharded requested, no ICU shipped
config.globalizationMode = 'Sharded';
// after: ship the shards or go invariant
config.resources.icu = [{ name:'icudt_EFIGS.dat', virtualPath:'icudt_EFIGS.dat' }];

// before starting the runtime
const needsIcu = ['Custom','All','Sharded'].includes(config.globalizationMode);
if (needsIcu && !(config.resources?.icu?.length))
    throw new Error(`${config.globalizationMode} mode requires ICU data`);

When it happens

Trigger: Setting config.globalizationMode = GlobalizationMode.Sharded (or All/Custom) without including any ICU .dat files in resources; misconfigured build that strips ICU data but requests a real ICU mode; a custom ICU archive path that does not resolve.

Common situations: Trying to reduce download size by sharding ICU but the shards are not published in the output; setting GlobalizationMode.Custom without providing the custom ICU asset; upgrading the SDK changed default behavior.

Related errors

• Failed to load ICU data
• Can't use moduleFactory callback of createDotnetRuntime…
• Failed to initialize ICU data
• Invalid config, resources is not set
• Loader configuration error: 'mainAssemblyName' is required.

AI-assisted analysis of dotnet/runtime@60108ba66e (2026-08-10). Data as JSON: /api/errors/f1bdcfcbc8f766de. Report an issue: GitHub.

Appendix: source

Thrown at src/mono/browser/runtime/loader/icu.ts:23

import { GlobalizationMode, MonoConfig } from "../types";
import { ENVIRONMENT_IS_WEB, loaderHelpers } from "./globals";
import { mono_log_info, mono_log_debug } from "./logging";

export function init_globalization () {
    loaderHelpers.preferredIcuAsset = getIcuResourceName(loaderHelpers.config);
    let invariantMode = loaderHelpers.config.globalizationMode == GlobalizationMode.Invariant;

    if (!invariantMode) {
        if (loaderHelpers.preferredIcuAsset) {
            mono_log_debug("ICU data archive(s) available, disabling invariant mode");
        } else if (loaderHelpers.config.globalizationMode !== GlobalizationMode.Custom && loaderHelpers.config.globalizationMode !== GlobalizationMode.All && loaderHelpers.config.globalizationMode !== GlobalizationMode.Sharded) {
            mono_log_debug("ICU data archive(s) not available, using invariant globalization mode");
            invariantMode = true;
            loaderHelpers.preferredIcuAsset = null;
        } else {
            const msg = "invariant globalization mode is inactive and no ICU data archives are available";
            mono_log_error(`ERROR: ${msg}`);
            throw new Error(msg);
        }
    }

    const invariantEnv = "DOTNET_SYSTEM_GLOBALIZATION_INVARIANT";
    const env_variables = loaderHelpers.config.environmentVariables!;
    if (env_variables[invariantEnv] === undefined && invariantMode) {
        env_variables[invariantEnv] = "1";
    }
    if (env_variables["TZ"] === undefined) {
        try {
            // this call is relatively expensive, so we call it during download of other assets
            const timezone = Intl.DateTimeFormat().resolvedOptions().timeZone || null;
            if (timezone) {
                env_variables!["TZ"] = timezone;
            }
        } catch {
            mono_log_info("failed to detect timezone, will fallback to UTC");
        }

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