Use String#truncate_bytes inside Multibyte::Chars#limit

activesupport/lib/active_support/multibyte/chars.rb

@@ -122,7 +122,7 @@ def reverse
       #
       #   'こんにちは'.mb_chars.limit(7).to_s # => "こん"
       def limit(limit)
-        slice(0...translate_offset(limit))
+        truncate_bytes(limit, omission: nil)
       end
 
       # Capitalizes the first letter of every word, when possible.
@@ -208,18 +208,6 @@ def as_json(options = nil) #:nodoc:
 
       private
 
-        def translate_offset(byte_offset)
-          return nil if byte_offset.nil?
-          return 0   if @wrapped_string == ""
-
-          begin
-            @wrapped_string.byteslice(0...byte_offset).unpack("U*").length
-          rescue ArgumentError
-            byte_offset -= 1
-            retry
-          end
-        end
-
         def chars(string)
           self.class.new(string)
         end

activesupport/test/multibyte_chars_test.rb

@@ -785,21 +785,3 @@ def string_from_classes(classes)
       end.pack("U*")
     end
 end
-
-class MultibyteInternalsTest < ActiveSupport::TestCase
-  include MultibyteTestHelpers
-
-  test "Chars translates a character offset to a byte offset" do
-    example = chars("Puisque c'était son erreur, il m'a aidé")
-    [
-      [0, 0],
-      [3, 3],
-      [12, 11],
-      [14, 13],
-      [41, 39]
-    ].each do |byte_offset, character_offset|
-      assert_equal character_offset, example.send(:translate_offset, byte_offset),
-        "Expected byte offset #{byte_offset} to translate to #{character_offset}"
-    end
-  end
-end