feat: add avoid_hardcoded_unicode lint rule (generalized from avoid_hardcoded_japanese)

packages/altive_lints/example/lints/avoid_hardcoded_unicode.dart

@@ -0,0 +1,12 @@
+// Check the `avoid_hardcoded_unicode` rule.
+
+// expect_lint: avoid_hardcoded_unicode
+const japanese = 'こんにちは';
+// expect_lint: avoid_hardcoded_unicode
+const russian = 'Ошибка';
+// expect_lint: avoid_hardcoded_unicode
+const spanish = '¡Hola!';
+
+const ascii = 'Hello!';
+const numbers = '12345';
+const symbols = '!@#%&*()';

packages/altive_lints/example/lints/avoid_hardcoded_unicode_test.dart

@@ -0,0 +1,7 @@
+// Check the `avoid_hardcoded_unicode` rule.
+// This file ends with the name `_test.dart`,
+// so it should be exempt from the warning.
+
+const japanese = 'こんにちは';
+const russian = 'Ошибка';
+const ascii = 'Hello!';

packages/altive_lints/example/test/avoid_hardcoded_unicode.dart

@@ -0,0 +1,6 @@
+// Check the `avoid_hardcoded_unicode` rule.
+// It should exclude warnings for the entire `test` directory.
+
+const japanese = 'こんにちは';
+const russian = 'Ошибка';
+const ascii = 'Hello!';

packages/altive_lints/lib/all_lint_rules.yaml

@@ -232,3 +232,4 @@ linter:
     - use_truncating_division
     - valid_regexps
     - void_checks
+    - avoid_hardcoded_unicode

packages/altive_lints/lib/altive_lints.dart

@@ -6,6 +6,7 @@ import 'src/assists/wrap_with_macro_template_document_comment.dart';
 import 'src/lints/avoid_consecutive_sliver_to_box_adapter.dart';
 import 'src/lints/avoid_hardcoded_color.dart';
 import 'src/lints/avoid_hardcoded_japanese.dart';
+import 'src/lints/avoid_hardcoded_unicode.dart';
 import 'src/lints/avoid_shrink_wrap_in_list_view.dart';
 import 'src/lints/avoid_single_child.dart';
 import 'src/lints/prefer_clock_now.dart';
@@ -22,6 +23,7 @@ class _AltivePlugin extends PluginBase {
         const AvoidConsecutiveSliverToBoxAdapter(),
         const AvoidHardcodedColor(),
         const AvoidHardcodedJapanese(),
+        const AvoidHardcodedUnicode(),
         const AvoidShrinkWrapInListView(),
         const AvoidSingleChild(),
         const PreferClockNow(),

packages/altive_lints/lib/src/lints/avoid_hardcoded_unicode.dart

@@ -0,0 +1,84 @@
+import 'package:analyzer/error/listener.dart';
+import 'package:custom_lint_builder/custom_lint_builder.dart';
+
+import '../utils/files_utils.dart';
+
+/// An `avoid_hardcoded_unicode` rule which detects
+/// and reports hardcoded string literals containing characters
+/// outside a configurable ASCII range (default: 0x20-0x7E).
+///
+/// This rule ensures that all user-facing text is
+/// properly internationalized and avoids hardcoded non-ASCII text.
+///
+/// ### Example
+///
+/// #### BAD:
+///
+/// ```dart
+/// final message = 'こんにちは'; // LINT
+/// print('Ошибка'); // LINT
+/// print('¡Hola!'); // LINT
+/// ```
+///
+/// #### GOOD:
+///
+/// ```dart
+/// final message = AppLocalizations.of(context).hello;
+/// print(AppLocalizations.of(context).errorOccurred);
+/// ```
+///
+class AvoidHardcodedUnicode extends DartLintRule {
+  /// Creates a new instance of [AvoidHardcodedUnicode].
+  const AvoidHardcodedUnicode({
+    this.allowedRangeStart = 0x20,
+    this.allowedRangeEnd = 0x7E,
+  }) : super(code: _code);
+
+  final int allowedRangeStart;
+  final int allowedRangeEnd;
+
+  static const _code = LintCode(
+    name: 'avoid_hardcoded_unicode',
+    problemMessage: 'This string contains hardcoded non-ASCII (Unicode) characters.\n'
+        'Ensure all user-facing text is properly internationalized.',
+  );
+
+  @override
+  void run(
+    CustomLintResolver resolver,
+    ErrorReporter reporter,
+    CustomLintContext context,
+  ) {
+    if (isTestFile(resolver.source)) {
+      return;
+    }
+    context.registry.addSimpleStringLiteral((node) {
+      final stringValue = node.stringValue;
+      if (stringValue == null) {
+        return;
+      }
+      if (_containsDisallowedUnicode(stringValue)) {
+        reporter.atNode(node, _code);
+      }
+    });
+
+    context.registry.addStringInterpolation((node) {
+      final stringValue = node.toSource();
+      if (_containsDisallowedUnicode(stringValue)) {
+        reporter.atNode(node, _code);
+      }
+    });
+  }
+
+  /// Checks if the string contains any character outside the allowed ASCII range.
+  bool _containsDisallowedUnicode(String value) {
+    for (final codeUnit in value.codeUnits) {
+      if (codeUnit < allowedRangeStart || codeUnit > allowedRangeEnd) {
+        // Allow common escape sequences (e.g., \n, \t)
+        if (codeUnit == 0x0A || codeUnit == 0x0D || codeUnit == 0x09) continue;
+        return true;
+      }
+    }
+    return false;
+  }
+}