diff --git a/i18n_guardian/diff/diff_generator.py b/i18n_guardian/diff/diff_generator.py
new file mode 100644
index 0000000..8d91851
--- /dev/null
+++ b/i18n_guardian/diff/diff_generator.py
@@ -0,0 +1,168 @@
+"""Diff generation for i18n fixes."""
+
+import difflib
+from dataclasses import dataclass, field
+from pathlib import Path
+from typing import List, Optional
+
+from rich.console import Console
+from rich.syntax import Syntax
+
+
+@dataclass
+class DiffChange:
+    """Represents a single change in a diff."""
+
+    file_path: Path
+    original_line: int
+    original_text: str
+    new_text: str
+    new_line: Optional[int] = None
+
+
+@dataclass
+class DiffResult:
+    """Result of a diff operation."""
+
+    changes: List[DiffChange] = field(default_factory=list)
+    files_modified: int = 0
+    total_changes: int = 0
+
+
+class DiffGenerator:
+    """Generate diffs for i18n fixes."""
+
+    def __init__(self, color: bool = True) -> None:
+        self.color = color
+        self.console = Console()
+
+    def generate_diff(
+        self,
+        file_path: Path,
+        old_content: str,
+        new_content: str,
+    ) -> str:
+        """Generate a unified diff between old and new content."""
+        diff = difflib.unified_diff(
+            old_content.splitlines(keepends=True),
+            new_content.splitlines(keepends=True),
+            fromfile=str(file_path),
+            tofile=str(file_path),
+            n=3,
+        )
+        return "".join(diff)
+
+    def preview_diff(self, diff: str) -> None:
+        """Preview a diff using Rich."""
+        if self.color:
+            self.console.print(Syntax(diff, "diff", line_numbers=True))
+        else:
+            self.console.print(diff)
+
+    def apply_diff(
+        self,
+        file_path: Path,
+        diff: str,
+        backup: bool = True,
+    ) -> bool:
+        """Apply a diff to a file."""
+        try:
+            if backup:
+                backup_path = file_path.with_suffix(".bak")
+                backup_path.write_text(file_path.read_text(encoding="utf-8"), encoding="utf-8")
+
+            lines = file_path.read_text(encoding="utf-8").splitlines(keepends=True)
+            diff_lines = diff.splitlines(keepends=True)
+
+            patched_lines = self._apply_diff_lines(lines, diff_lines)
+
+            new_content = "".join(patched_lines)
+            file_path.write_text(new_content, encoding="utf-8")
+
+            return True
+        except (OSError, UnicodeDecodeError) as e:
+            print(f"Error applying diff: {e}")
+            return False
+
+    def _apply_diff_lines(
+        self,
+        lines: List[str],
+        diff_lines: List[str],
+    ) -> List[str]:
+        """Apply diff lines to document."""
+        result = []
+
+        i = 0
+        j = 0
+
+        while j < len(diff_lines):
+            diff_line = diff_lines[j]
+
+            if diff_line.startswith("---") or diff_line.startswith("+++"):
+                j += 1
+                continue
+
+            if diff_line.startswith("@@"):
+                j += 1
+                continue
+
+            if diff_line.startswith("-"):
+                original_line = diff_line[1:]
+                added_content = ""
+                if "+" in original_line:
+                    parts = original_line.split("+", 1)
+                    original_line = parts[0]
+                    added_content = parts[1] if len(parts) > 1 else ""
+                while i < len(lines) and lines[i].rstrip("\n") != original_line.rstrip("\n"):
+                    result.append(lines[i])
+                    i += 1
+                if i < len(lines):
+                    i += 1
+                if added_content:
+                    result.append(added_content)
+                j += 1
+                continue
+
+            if diff_line.startswith("+"):
+                result.append(diff_line[1:])
+                j += 1
+                continue
+
+            if diff_line.startswith(" "):
+                result.append(lines[i] if i < len(lines) else diff_line[1:])
+                i += 1
+                j += 1
+                continue
+
+            j += 1
+
+        while i < len(lines):
+            result.append(lines[i])
+            i += 1
+
+        return result
+
+    def create_replacement(
+        self,
+        original_text: str,
+        replacement: str,
+        i18n_function: str = "t",
+    ) -> str:
+        """Create a replacement string with i18n function call."""
+        escaped = original_text.replace("\\", "\\\\").replace('"', '\\"')
+        return f'{i18n_function}("{escaped}")'
+
+    def preview_change(
+        self,
+        file_path: Path,
+        original_text: str,
+        replacement: str,
+        line_number: int,
+    ) -> None:
+        """Preview a single change."""
+        diff = self.generate_diff(
+            file_path,
+            original_text,
+            original_text.replace(original_text, replacement, 1),
+        )
+        self.preview_diff(diff)