feat(cli): add pseudo-localization mode

packages/cli/src/cli/cmd/run/_types.ts

@@ -53,5 +53,6 @@ export const flagsSchema = z.object({
   watch: z.boolean().default(false),
   debounce: z.number().positive().default(5000), // 5 seconds default
   sound: z.boolean().optional(),
+  pseudo: z.boolean().optional(),
 });
 export type CmdRunFlags = z.infer<typeof flagsSchema>;

packages/cli/src/cli/cmd/run/index.ts

@@ -118,6 +118,10 @@ export default new Command()
     "--sound",
     "Play audio feedback when translations complete (success or failure sounds)",
   )
+  .option(
+    "--pseudo",
+    "Enable pseudo-localization mode: automatically pseudo-translates all extracted strings with accented characters and visual markers without calling any external API. Useful for testing UI internationalization readiness",
+  )
   .action(async (args) => {
     let authId: string | null = null;
     try {

packages/cli/src/cli/cmd/run/setup.ts

@@ -50,10 +50,8 @@ export default async function setup(input: CmdRunContext) {
       {
         title: "Selecting localization provider",
         task: async (ctx, task) => {
-          ctx.localizer = createLocalizer(
-            ctx.config?.provider,
-            ctx.flags.apiKey,
-          );
+          const provider = ctx.flags.pseudo ? "pseudo" : ctx.config?.provider;
+          ctx.localizer = createLocalizer(provider, ctx.flags.apiKey);
           if (!ctx.localizer) {
             throw new Error(
               "Could not create localization provider. Please check your i18n.json configuration.",
@@ -62,12 +60,15 @@ export default async function setup(input: CmdRunContext) {
           task.title =
             ctx.localizer.id === "Lingo.dev"
               ? `Using ${chalk.hex(colors.green)(ctx.localizer.id)} provider`
-              : `Using raw ${chalk.hex(colors.yellow)(ctx.localizer.id)} API`;
+              : ctx.localizer.id === "pseudo"
+                ? `Using ${chalk.hex(colors.blue)("pseudo")} mode for testing`
+                : `Using raw ${chalk.hex(colors.yellow)(ctx.localizer.id)} API`;
         },
       },
       {
         title: "Checking authentication",
-        enabled: (ctx) => ctx.localizer?.id === "Lingo.dev",
+        enabled: (ctx) =>
+          ctx.localizer?.id === "Lingo.dev" && !ctx.flags.pseudo,
         task: async (ctx, task) => {
           const authStatus = await ctx.localizer!.checkAuth();
           if (!authStatus.authenticated) {
@@ -95,6 +96,7 @@ export default async function setup(input: CmdRunContext) {
         title: "Initializing localization provider",
         async task(ctx, task) {
           const isLingoDotDev = ctx.localizer!.id === "Lingo.dev";
+          const isPseudo = ctx.localizer!.id === "pseudo";
 
           const subTasks = isLingoDotDev
             ? [
@@ -103,12 +105,18 @@ export default async function setup(input: CmdRunContext) {
                 "Glossary enabled",
                 "Quality assurance enabled",
               ].map((title) => ({ title, task: () => {} }))
-            : [
-                "Skipping brand voice",
-                "Skipping glossary",
-                "Skipping translation memory",
-                "Skipping quality assurance",
-              ].map((title) => ({ title, task: () => {}, skip: true }));
+            : isPseudo
+              ? [
+                  "Pseudo-localization mode active",
+                  "Character replacement configured",
+                  "No external API calls",
+                ].map((title) => ({ title, task: () => {} }))
+              : [
+                  "Skipping brand voice",
+                  "Skipping glossary",
+                  "Skipping translation memory",
+                  "Skipping quality assurance",
+                ].map((title) => ({ title, task: () => {}, skip: true }));
 
           return task.newListr(subTasks, {
             concurrent: true,

packages/cli/src/cli/localizer/_types.ts

@@ -16,7 +16,7 @@ export type LocalizerProgressFn = (
 ) => void;
 
 export interface ILocalizer {
-  id: "Lingo.dev" | NonNullable<I18nConfig["provider"]>["id"];
+  id: "Lingo.dev" | "pseudo" | NonNullable<I18nConfig["provider"]>["id"];
   checkAuth: () => Promise<{
     authenticated: boolean;
     username?: string;

packages/cli/src/cli/localizer/index.ts

@@ -2,12 +2,17 @@ import { I18nConfig } from "@lingo.dev/_spec";
 
 import createLingoDotDevLocalizer from "./lingodotdev";
 import createExplicitLocalizer from "./explicit";
+import createPseudoLocalizer from "./pseudo";
 import { ILocalizer } from "./_types";
 
 export default function createLocalizer(
-  provider: I18nConfig["provider"],
+  provider: I18nConfig["provider"] | "pseudo" | null | undefined,
   apiKey?: string,
 ): ILocalizer {
+  if (provider === "pseudo") {
+    return createPseudoLocalizer();
+  }
+
   if (!provider) {
     return createLingoDotDevLocalizer(apiKey);
   } else {

packages/cli/src/cli/localizer/pseudo.ts

@@ -0,0 +1,37 @@
+import { ILocalizer, LocalizerData } from "./_types";
+import { pseudoLocalizeObject } from "../../utils/pseudo-localize";
+
+/**
+ * Creates a pseudo-localizer that doesn't call any external API.
+ * Instead, it performs character replacement with accented versions,
+ * useful for testing UI internationalization readiness.
+ */
+export default function createPseudoLocalizer(): ILocalizer {
+  return {
+    id: "pseudo",
+    checkAuth: async () => {
+      return {
+        authenticated: true,
+      };
+    },
+    localize: async (input: LocalizerData, onProgress) => {
+      // Nothing to translate – return the input as-is.
+      if (!Object.keys(input.processableData).length) {
+        return input;
+      }
+
+      // Pseudo-localize all strings in the processable data
+      const processedData = pseudoLocalizeObject(input.processableData, {
+        addMarker: true,
+        addLengthMarker: false,
+      });
+
+      // Call progress callback if provided, simulating completion
+      if (onProgress) {
+        onProgress(100, input.processableData, processedData);
+      }
+
+      return processedData;
+    },
+  };
+}

packages/cli/src/utils/pseudo-localize.spec.ts

@@ -0,0 +1,124 @@
+import { describe, it, expect } from "vitest";
+import { pseudoLocalize, pseudoLocalizeObject } from "./pseudo-localize";
+
+describe("pseudoLocalize", () => {
+  it("should replace characters with accented versions", () => {
+    const result = pseudoLocalize("hello", { addMarker: false });
+    expect(result).toBe("ĥèļļø");
+  });
+
+  it("should add marker by default", () => {
+    const result = pseudoLocalize("hello");
+    expect(result).toBe("ĥèļļø⚡");
+  });
+
+  it("should not add marker when disabled", () => {
+    const result = pseudoLocalize("hello", { addMarker: false });
+    expect(result).not.toContain("⚡");
+  });
+
+  it("should handle uppercase letters", () => {
+    const result = pseudoLocalize("HELLO", { addMarker: false });
+    expect(result).toBe("ĤÈĻĻØ");
+  });
+
+  it("should preserve non-alphabetic characters", () => {
+    const result = pseudoLocalize("Hello123!", { addMarker: false });
+    expect(result).toBe("Ĥèļļø123!");
+  });
+
+  it("should handle empty strings", () => {
+    const result = pseudoLocalize("");
+    expect(result).toBe("");
+  });
+
+  it("should handle strings with spaces", () => {
+    const result = pseudoLocalize("Hello World", { addMarker: false });
+    expect(result).toBe("Ĥèļļø Ŵøŕļð");
+  });
+
+  it("should add length expansion when enabled", () => {
+    const original = "hello";
+    const result = pseudoLocalize(original, {
+      addMarker: false,
+      addLengthMarker: true,
+      lengthExpansion: 30,
+    });
+    // 30% expansion of 5 chars = 2 extra chars (rounded up)
+    expect(result.length).toBeGreaterThan("ĥèļļø".length);
+  });
+
+  it("should handle example from feature proposal", () => {
+    const result = pseudoLocalize("Submit");
+    expect(result).toContain("⚡");
+    expect(result.startsWith("Š")).toBe(true);
+  });
+
+  it("should handle longer text", () => {
+    const result = pseudoLocalize("Welcome back!");
+    expect(result).toBe("Ŵèļçømè ƀãçķ!⚡");
+  });
+});
+
+describe("pseudoLocalizeObject", () => {
+  it("should pseudo-localize string values", () => {
+    const obj = { greeting: "hello" };
+    const result = pseudoLocalizeObject(obj, { addMarker: false });
+    expect(result.greeting).toBe("ĥèļļø");
+  });
+
+  it("should handle nested objects", () => {
+    const obj = {
+      en: {
+        greeting: "hello",
+        farewell: "goodbye",
+      },
+    };
+    const result = pseudoLocalizeObject(obj, { addMarker: false });
+    expect(result.en.greeting).toBe("ĥèļļø");
+    expect(result.en.farewell).toContain("ĝ");
+  });
+
+  it("should handle arrays", () => {
+    const obj = {
+      messages: ["hello", "world"],
+    };
+    const result = pseudoLocalizeObject(obj, { addMarker: false });
+    expect(Array.isArray(result.messages)).toBe(true);
+    expect(result.messages[0]).toBe("ĥèļļø");
+  });
+
+  it("should preserve non-string values", () => {
+    const obj = {
+      greeting: "hello",
+      count: 42,
+      active: true,
+      nothing: null,
+    };
+    const result = pseudoLocalizeObject(obj, { addMarker: false });
+    expect(result.greeting).toBe("ĥèļļø");
+    expect(result.count).toBe(42);
+    expect(result.active).toBe(true);
+    expect(result.nothing).toBe(null);
+  });
+
+  it("should handle complex nested structures", () => {
+    const obj = {
+      ui: {
+        buttons: {
+          submit: "Submit",
+          cancel: "Cancel",
+        },
+        messages: ["error", "warning"],
+      },
+    };
+    const result = pseudoLocalizeObject(obj, { addMarker: false });
+    expect(result.ui.buttons.submit).toContain("Š");
+    expect(result.ui.messages[0]).toContain("è");
+  });
+
+  it("should handle empty objects", () => {
+    const result = pseudoLocalizeObject({}, { addMarker: false });
+    expect(result).toEqual({});
+  });
+});