Fixed a typo in the render paragraph locale setter (#18189)

packages/flutter/lib/src/rendering/paragraph.dart

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui' as ui show Gradient, Shader, TextBox, Locale;
+import 'dart:ui' as ui show Gradient, Shader, TextBox;
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
@@ -44,7 +44,7 @@ class RenderParagraph extends RenderBox {
     TextOverflow overflow = TextOverflow.clip,
     double textScaleFactor = 1.0,
     int maxLines,
-    ui.Locale locale,
+    Locale locale,
   }) : assert(text != null),
        assert(text.debugAssertIsValid()),
        assert(textAlign != null),
@@ -176,11 +176,19 @@ class RenderParagraph extends RenderBox {
     markNeedsLayout();
   }
 
-  ui.Locale get locale => _textPainter.locale;
-  set locale(ui.Locale value) {
+  /// Used by this paragraph's internal [TextPainter] to select a locale-specific
+  /// font.
+  ///
+  /// In some cases the same Unicode character may be rendered differently depending
+  /// on the locale. For example the '骨' character is rendered differently in
+  /// the Chinese and Japanese locales. In these cases the [locale] may be used
+  /// to select a locale-specific font.
+  Locale get locale => _textPainter.locale;
+  /// The value may be null.
+  set locale(Locale value) {
     if (_textPainter.locale == value)
       return;
-    _textPainter.locale = locale;
+    _textPainter.locale = value;
     _overflowShader = null;
     markNeedsLayout();
   }
@@ -286,6 +294,7 @@ class RenderParagraph extends RenderBox {
             text: new TextSpan(style: _textPainter.text.style, text: '\u2026'),
             textDirection: textDirection,
             textScaleFactor: textScaleFactor,
+            locale: locale,
           )..layout();
           if (didOverflowWidth) {
             double fadeEnd, fadeStart;

packages/flutter/lib/src/widgets/basic.dart

@@ -235,7 +235,7 @@ class ShaderMask extends SingleChildRenderObjectWidget {
   /// it can customize the shader to the size and location of the child.
   ///
   /// Typically this will use a [LinearGradient], [RadialGradient], or
-  /// [SweepGradient] to create the [dart:ui.Shader], though the 
+  /// [SweepGradient] to create the [dart:ui.Shader], though the
   /// [dart:ui.ImageShader] class could also be used.
   final ShaderCallback shaderCallback;
 
@@ -4289,6 +4289,7 @@ class RichText extends LeafRenderObjectWidget {
     this.overflow = TextOverflow.clip,
     this.textScaleFactor = 1.0,
     this.maxLines,
+    this.locale,
   }) : assert(text != null),
        assert(textAlign != null),
        assert(softWrap != null),
@@ -4341,6 +4342,15 @@ class RichText extends LeafRenderObjectWidget {
   /// edge of the box.
   final int maxLines;
 
+  /// Used to select a font when the same Unicode character can
+  /// be rendered differently, depending on the locale.
+  ///
+  /// It's rarely necessary to set this property. By default its value
+  /// is inherited from the enclosing app with `Localizations.localeOf(context)`.
+  ///
+  /// See [RenderParagraph.locale] for more information.
+  final Locale locale;
+
   @override
   RenderParagraph createRenderObject(BuildContext context) {
     assert(textDirection != null || debugCheckHasDirectionality(context));
@@ -4351,7 +4361,7 @@ class RichText extends LeafRenderObjectWidget {
       overflow: overflow,
       textScaleFactor: textScaleFactor,
       maxLines: maxLines,
-      locale: Localizations.localeOf(context, nullOk: true),
+      locale: locale ?? Localizations.localeOf(context, nullOk: true),
     );
   }
 
@@ -4366,7 +4376,7 @@ class RichText extends LeafRenderObjectWidget {
       ..overflow = overflow
       ..textScaleFactor = textScaleFactor
       ..maxLines = maxLines
-      ..locale = Localizations.localeOf(context, nullOk: true);
+      ..locale = locale ?? Localizations.localeOf(context, nullOk: true);
   }
 
   @override

packages/flutter/test/rendering/paragraph_test.dart

@@ -310,4 +310,19 @@ void main() {
       ),
     );
   });
+
+  test('locale setter', () {
+    // Regression test for https://github.com/flutter/flutter/issues/18175
+
+    final RenderParagraph paragraph = new RenderParagraph(
+      const TextSpan(text: _kText),
+      locale: const Locale('zh', 'HK'),
+      textDirection: TextDirection.ltr,
+    );
+    expect(paragraph.locale, const Locale('zh', 'HK'));
+
+    paragraph.locale = const Locale('ja', 'JP');
+    expect(paragraph.locale, const Locale('ja', 'JP'));
+  });
+
 }