feat: add plain text (.txt) file support

## Changed
- Fix [locale] at start of include paths in config validation
- Fix no-this-alias lint error in ts.parser
- Direct translation now parses .txt files line-by-line instead of as raw text

## New
- Add TxtParser for line-by-line .txt file translation with structure preservation
- Add TXT format to parser factory, supported types, and config schema
- Add txt parser unit tests (30 tests) and integration tests (10 tests)
- Add plain text files documentation and format guide

Author: Starllordz

docs/README.md

@@ -55,3 +55,4 @@ The `lara.yaml` configuration file controls how Lara CLI works with your project
 - [Xcode Strings Files Guide](config/files/xcode-strings-files.md) - Complete guide for Xcode .strings files
 - [Xcode Stringsdict Files Guide](config/files/xcode-stringsdict-files.md) - Complete guide for Xcode .stringsdict plural files
 - [Xcode String Catalogs Guide](config/files/xcode-xcstrings-files.md) - Complete guide for Xcode .xcstrings String Catalogs
+- [TXT Files Guide](config/files/txt-files.md) - Complete guide for plain text files

docs/commands/translate.md

@@ -163,8 +163,8 @@ lara-cli translate --file "messages.json" --source en --target fr --output "mess
 
 #### Structured vs Plain Text Files
 
-- **Structured files** (JSON, PO, XML, Markdown, and other [supported formats](../config/formats.md)): Parsed key-by-key, preserving file structure, formatting, and non-string values.
-- **Plain text files** (`.txt` and unsupported extensions): The entire file content is translated as a single block of text.
+- **Structured files** (JSON, PO, XML, Markdown, TXT, and other [supported formats](../config/formats.md)): Parsed and translated preserving file structure, formatting, and non-string values. For `.txt` files, each non-empty line is translated independently while empty lines are preserved.
+- **Unsupported extensions**: The entire file content is translated as a single block of text.
 
 ### Direct Translation Options
 

docs/config/files/txt-files.md

@@ -0,0 +1,284 @@
+# Plain Text Files Configuration
+
+This guide explains how to use Lara CLI with plain text (`.txt`) files for internationalization.
+
+## Configuration
+
+To configure plain text files in your `lara.yaml`:
+
+```yaml
+files:
+  txt:
+    include:
+      - 'texts/[locale]/*.txt'
+    exclude: []
+    lockedKeys: []
+    ignoredKeys: []
+```
+
+### File Path Patterns
+
+Plain text files can be configured using glob patterns with the `[locale]` placeholder:
+
+#### Locale-Based Directory Pattern (Recommended)
+
+Organize text files by locale in separate directories:
+
+```yaml
+files:
+  txt:
+    include:
+      - 'texts/[locale]/*.txt'
+      - 'content/[locale]/**/*.txt'
+```
+
+This pattern expects separate files per locale:
+
+```text
+texts/
+  ├── en/
+  │   ├── messages.txt
+  │   ├── notifications.txt
+  │   └── emails/
+  │       └── welcome.txt
+  ├── es/
+  │   ├── messages.txt
+  │   ├── notifications.txt
+  │   └── emails/
+  │       └── welcome.txt
+  └── fr/
+      ├── messages.txt
+      ├── notifications.txt
+      └── emails/
+          └── welcome.txt
+```
+
+#### Locale in Filename Pattern
+
+If you use locale codes in filenames:
+
+```yaml
+files:
+  txt:
+    include:
+      - 'texts/[locale].txt'
+```
+
+This matches files like:
+
+- `texts/en.txt`
+- `texts/es.txt`
+- `texts/fr.txt`
+
+## Plain Text File Structure
+
+### Basic Structure
+
+Lara CLI extracts text content from plain text files on a line-by-line basis:
+
+```text
+Welcome to our application
+Please sign in to continue
+Thank you for your purchase
+```
+
+Each non-empty line becomes an independent translatable segment. Empty lines are preserved structurally but not translated.
+
+### How Lines Are Extracted
+
+Lara CLI extracts non-empty lines sequentially and assigns them keys:
+
+- `line_0` - First non-empty line
+- `line_1` - Second non-empty line
+- `line_2` - Third non-empty line
+- etc.
+
+**Example:**
+
+```text
+Hello World
+
+Welcome to our application.
+
+Thank you for using our product.
+```
+
+Extracted segments:
+
+- `line_0`: "Hello World"
+- `line_1`: "Welcome to our application."
+- `line_2`: "Thank you for using our product."
+
+Empty lines between content are preserved in the translated output but are not assigned keys.
+
+### What Is Translated
+
+- Each non-empty line (lines containing at least one non-whitespace character)
+
+### What Is Preserved (Not Translated)
+
+- Empty lines (used as structural separators)
+- Whitespace-only lines
+- Leading and trailing whitespace within content lines
+- Trailing newlines at end of file
+
+## Key Path Format
+
+When using `lockedKeys` or `ignoredKeys` with plain text files, use line-based keys:
+
+```yaml
+files:
+  txt:
+    include:
+      - 'texts/[locale]/*.txt'
+    lockedKeys:
+      - 'line_0'  # First line (e.g., title)
+      - 'line_5'  # Specific line
+    ignoredKeys:
+      - 'line_10' # Ignore specific line
+```
+
+**Note:** Line indices are position-based (counting only non-empty lines) and depend on the document structure. Use with caution as document changes may shift line indices.
+
+## Complete Example
+
+Here's a complete configuration example:
+
+```yaml
+version: '1.0.0'
+
+project:
+  instruction: 'Simple, clear language for UI text'
+
+locales:
+  source: en
+  target:
+    - es
+    - fr
+    - de
+    - it
+
+memories:
+  - mem_abc123
+
+glossaries:
+  - gls_xyz789
+
+files:
+  txt:
+    include:
+      - 'texts/[locale]/messages.txt'
+      - 'texts/[locale]/notifications.txt'
+    exclude:
+      - 'texts/[locale]/draft-*.txt'
+    fileInstructions:
+      - path: 'texts/[locale]/notifications.txt'
+        instruction: 'Short notification messages, concise and clear'
+```
+
+## Working with Existing Text Files
+
+If you already have text files organized by locale:
+
+1. **Run `lara-cli init`** to create your configuration
+2. **Ensure your file paths match the `include` patterns**
+3. **Run `lara-cli translate`**
+4. **Continue developing** - Lara CLI tracks changes via checksums and only translates what's new or modified
+
+If your text files aren't organized by locale yet:
+
+1. **Organize files** into locale-based directories or use locale prefixes in filenames
+2. **Update your `lara.yaml`** to match your file structure
+3. **Run `lara-cli translate`**
+
+## Best Practices
+
+### 1. Organize by Locale
+
+Keep separate text files for each locale:
+
+```text
+texts/
+  ├── en/
+  │   └── messages.txt
+  ├── es/
+  │   └── messages.txt
+  └── fr/
+      └── messages.txt
+```
+
+### 2. One Translatable Unit Per Line
+
+Each line should contain one independent piece of text:
+
+```text
+Welcome to our app
+Sign in to continue
+Forgot your password?
+```
+
+Avoid splitting a single sentence across multiple lines, as each line is translated independently.
+
+### 3. Use Empty Lines as Separators
+
+Group related content with empty lines for readability:
+
+```text
+Welcome to our app
+
+Sign in to continue
+Create a new account
+
+Need help?
+Contact support
+```
+
+### 4. Use Consistent Structure
+
+Keep the same line structure across all locale files to ensure translations align correctly.
+
+### 5. Leverage Instructions
+
+Use file-level instructions for better translation quality:
+
+```yaml
+files:
+  txt:
+    include:
+      - 'texts/[locale]/*.txt'
+    fileInstructions:
+      - path: 'texts/[locale]/ui-messages.txt'
+        instruction: 'Short UI labels and button text, keep concise'
+      - path: 'texts/[locale]/emails.txt'
+        instruction: 'Email content, professional and friendly tone'
+```
+
+## Limitations
+
+### File Format
+
+- Each non-empty line is treated as an independent translatable unit
+- No support for multi-line paragraphs (each line is a separate segment)
+- No support for key-value pairs (use JSON or PO for structured translations)
+- No support for comments or metadata within the file
+
+### Supported Patterns
+
+- Locale-based directories: `texts/[locale]/*.txt`
+- Locale in filenames: `texts/[locale].txt`
+- Recursive patterns: `texts/[locale]/**/*.txt`
+- Files without `[locale]` placeholder are not supported
+
+### Line Indexing
+
+- Line indices (`line_0`, `line_1`, etc.) count only non-empty lines
+- Adding or removing lines shifts line indices
+- Use `lockedKeys` and `ignoredKeys` carefully with line indices
+- Consider the document structure when using line-based keys
+
+## Related Documentation
+
+- [Supported Formats](../formats.md) - Overview of all supported file formats
+- [Files Configuration](../files.md) - General file configuration options
+- [Instructions](../instructions.md) - How to use translation instructions
+- [Locales](../locales.md) - Supported locale codes

docs/config/formats.md

@@ -15,6 +15,7 @@ Lara CLI supports multiple internationalization file formats. The appropriate pa
 | **Xcode Strings** | `.strings`   | Xcode .strings key-value localization files for iOS/macOS applications             | [Xcode Strings Files Guide](./files/xcode-strings-files.md) |
 | **Xcode Stringsdict** | `.stringsdict` | Xcode .stringsdict plist files with plural rules for iOS/macOS applications    | [Xcode Stringsdict Files Guide](./files/xcode-stringsdict-files.md) |
 | **Xcode String Catalogs** | `.xcstrings` | Xcode String Catalogs (Xcode 15+), all locales in a single JSON file       | [Xcode String Catalogs Guide](./files/xcode-xcstrings-files.md) |
+| **Plain Text**    | `.txt`        | Plain text files with one translatable segment per line                     | [TXT Files Guide](./files/txt-files.md)  |
 
 ## How It Works
 
@@ -29,6 +30,7 @@ The file format is automatically detected based on the file extension:
 - Files ending with `.strings` are parsed as Xcode .strings localization files
 - Files ending with `.stringsdict` are parsed as Xcode .stringsdict plural files
 - Files ending with `.xcstrings` are parsed as Xcode String Catalogs (all locales in one file)
+- Files ending with `.txt` are parsed as plain text files
 
 You can configure multiple formats simultaneously in the same project by adding different format sections under the `files` configuration.
 
@@ -60,6 +62,9 @@ files:
   xcode-xcstrings:
     include:
       - 'Localizable.xcstrings'
+  txt:
+    include:
+      - 'texts/[locale]/messages.txt'
 ```
 
 ## Format-Specific Documentation
@@ -74,3 +79,4 @@ For detailed information about a specific format, see its dedicated documentatio
 - [Xcode Strings Files Guide](./files/xcode-strings-files.md) - Complete guide for Xcode .strings files
 - [Xcode Stringsdict Files Guide](./files/xcode-stringsdict-files.md) - Complete guide for Xcode .stringsdict plural files
 - [Xcode String Catalogs Guide](./files/xcode-xcstrings-files.md) - Complete guide for Xcode .xcstrings String Catalogs
+- [TXT Files Guide](./files/txt-files.md) - Complete guide for plain text files

src/__tests__/integration/direct-translate.integration.test.ts

@@ -190,8 +190,8 @@ describe('Direct Translation Integration Tests', () => {
     });
   });
 
-  describe('file mode - plain text', () => {
-    it('should translate a plain text file and output to stdout', async () => {
+  describe('file mode - txt files', () => {
+    it('should translate a txt file and output to stdout', async () => {
       const inputFile = path.join(testDir, 'hello.txt');
       await writeFile(inputFile, 'Hello, world!');
 
@@ -278,6 +278,29 @@ describe('Direct Translation Integration Tests', () => {
       ).rejects.toThrow();
     });
 
+    it('should translate multi-line txt file line-by-line', async () => {
+      const inputFile = path.join(testDir, 'multi.txt');
+      await writeFile(inputFile, 'Hello\n\nWelcome\nGoodbye\n');
+
+      await executeCommand(translateCommand, [
+        '--file',
+        inputFile,
+        '--source',
+        'en',
+        '--target',
+        'fr',
+      ]);
+
+      const stdoutCalls = stdoutWriteSpy.mock.calls.map((call: unknown[]) => String(call[0]));
+      const output = stdoutCalls.find((call: string) => call.includes('[fr]'));
+      expect(output).toBeDefined();
+      expect(output).toContain('[fr] Hello');
+      expect(output).toContain('[fr] Welcome');
+      expect(output).toContain('[fr] Goodbye');
+      // Verify empty lines are preserved
+      expect(output).toContain('\n\n');
+    });
+
     it('should work without a lara.yaml config file', async () => {
       expect(existsSync(path.join(testDir, 'lara.yaml'))).toBe(false);
 
@@ -298,6 +321,25 @@ describe('Direct Translation Integration Tests', () => {
     });
   });
 
+  describe('file mode - plain text fallback', () => {
+    it('should translate unsupported file extensions as plain text', async () => {
+      const inputFile = path.join(testDir, 'data.csv');
+      await writeFile(inputFile, 'Hello, world!');
+
+      await executeCommand(translateCommand, [
+        '--file',
+        inputFile,
+        '--source',
+        'en',
+        '--target',
+        'fr',
+      ]);
+
+      const stdoutCalls = stdoutWriteSpy.mock.calls.map((call: unknown[]) => call[0]);
+      expect(stdoutCalls).toContainEqual('[fr] Hello, world!');
+    });
+  });
+
   describe('file mode - structured files (JSON)', () => {
     it('should translate JSON file preserving structure', async () => {
       const inputFile = path.join(testDir, 'messages.json');