fix(ux): improve "target language required" error with clearer suggestions

Replace the confusing JSON config syntax in the error message with a
short message + suggestion pointing users to --to and deepl init.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: sjsyrek

CHANGELOG.md

@@ -7,6 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Improved
+- "No target language specified" error now shows clearer suggestions: `--to <lang>` example and `deepl init` instead of raw JSON config syntax
+
 ### Changed
 - Updated GitHub Actions (`actions/checkout`, `actions/setup-node`) from v4 to v6 across all CI workflows
 - Updated `@types/node` from v20 to v25

src/cli/commands/register-translate.ts

@@ -102,7 +102,8 @@ Examples:
             options.to = targetLangs[0];
           } else {
             throw new ValidationError(
-              'Target language is required. Use --to <language> or set a default with: deepl config set defaults.targetLangs \'["es"]\'',
+              'No target language specified.',
+              'Use --to <lang>:   deepl translate "Hello" --to de\n  Set a default:     deepl init',
             );
           }
         }

src/cli/commands/register-watch.ts

@@ -61,7 +61,8 @@ Examples:
             options.to = targetLangs.join(',');
           } else {
             throw new ValidationError(
-              'Target language is required. Use --to <language> or set a default with: deepl config set defaults.targetLangs \'["es"]\'',
+              'No target language specified.',
+              'Use --to <lang>:   deepl watch ./docs --to de\n  Set a default:     deepl init',
             );
           }
         }

src/cli/commands/watch.ts

@@ -78,7 +78,10 @@ export class WatchCommand {
     const targetLangs = options.to.split(',').map(lang => lang.trim()).filter(lang => lang.length > 0) as Language[];
 
     if (targetLangs.length === 0) {
-      throw new ValidationError('At least one target language is required. Use --to es,fr,de');
+      throw new ValidationError(
+        'No target language specified.',
+        'Use --to <lang>:   deepl watch ./docs --to es,fr,de\n  Set a default:     deepl init',
+      );
     }
 
     // Get git-staged files if requested

tests/e2e/cli-document-translation.e2e.test.ts

@@ -252,7 +252,7 @@ describe('Document Translation E2E', () => {
       const result = runCLIExpectError(`translate "${testFile}"`, 'test-key:fx');
 
       expect(result.status).toBeGreaterThan(0);
-      expect(result.output).toMatch(/required option.*--to|target.*language.*required|missing.*--to/i);
+      expect(result.output).toMatch(/required option.*--to|target.*language|No target language specified|missing.*--to/i);
     });
 
     it('should handle authentication errors gracefully', () => {

tests/e2e/cli-stdin-stdout.e2e.test.ts

@@ -102,7 +102,7 @@ describe('CLI Stdin/Stdout E2E', () => {
       const result = runCLIExpectError(`translate "${testFile}"`, { apiKey: 'test-key:fx' });
 
       expect(result.status).toBeGreaterThan(0);
-      expect(result.output).toMatch(/required option.*--to|missing.*--to|target language is required.*--to/i);
+      expect(result.output).toMatch(/required option.*--to|missing.*--to|target language.*--to|No target language specified/i);
     });
   });
 
@@ -215,7 +215,7 @@ describe('CLI Stdin/Stdout E2E', () => {
       const result = runCLIExpectError(`translate "${testFile}" --quiet`, { apiKey: 'test-key:fx' });
 
       expect(result.status).toBeGreaterThan(0);
-      expect(result.output).toMatch(/required option.*--to|target language is required.*--to/i);
+      expect(result.output).toMatch(/required option.*--to|target language.*--to|No target language specified/i);
     });
   });
 });

tests/e2e/cli-watch.e2e.test.ts

@@ -99,8 +99,8 @@ describe('Watch Command E2E', () => {
       try {
         const { status, output } = runCLIExpectError(`watch ${tmpDir} --dry-run`);
         expect(status).toBeGreaterThan(0);
-        expect(output).toContain('Target language is required');
-        expect(output).toContain('deepl config set');
+        expect(output).toContain('No target language specified.');
+        expect(output).toContain('deepl init');
       } finally {
         fs.rmSync(tmpDir, { recursive: true, force: true });
       }

tests/integration/cli-translate.integration.test.ts

@@ -108,7 +108,7 @@ describe('Translate CLI Integration', () => {
       } catch (error: any) {
         const output = error.stderr ?? error.stdout;
         expect(output).toMatch(/--to/);
-        expect(output).toMatch(/defaults\.targetLangs/);
+        expect(output).toMatch(/deepl init/);
       }
     });
 

tests/unit/translate-default-target.test.ts

@@ -163,9 +163,7 @@ describe('translate command default target language', () => {
 
       expect(handleErrorSpy).toHaveBeenCalled();
       const error = capturedError as Error;
-      expect(error.message).toContain('Target language is required');
-      expect(error.message).toContain('--to');
-      expect(error.message).toContain('defaults.targetLangs');
+      expect(error.message).toContain('No target language specified.');
     });
 
     it('should throw error when config has no targetLangs', async () => {
@@ -177,9 +175,7 @@ describe('translate command default target language', () => {
 
       expect(handleErrorSpy).toHaveBeenCalled();
       const error = capturedError as Error;
-      expect(error.message).toContain('Target language is required');
-      expect(error.message).toContain('--to');
-      expect(error.message).toContain('defaults.targetLangs');
+      expect(error.message).toContain('No target language specified.');
     });
 
     it('should work with stdin when --to is omitted and config has default', async () => {

tests/unit/watch-command.test.ts

@@ -387,7 +387,7 @@ describe('WatchCommand', () => {
         watchCommand.watch('/some/file.md', {
           to: '',
         })
-      ).rejects.toThrow('At least one target language is required');
+      ).rejects.toThrow('No target language specified.');
     });
 
     it('should display initial watch message with all options', async () => {