title: Multi-byte characters and tr command
body: <p>I am trying to convert some single-byte characters into multi-byte characters using <code>tr</code>.</p>
  
  <p>When I have just one character to convert, conversion works:</p>
  
  <pre><code>"\\".tr('\\', '＼')
  # =&gt; "＼"
  </code></pre>
  
  <p>but if I add some more characters, the characters are not detected:</p>
  
  <pre><code>"\\".tr("\\¥'", "＼￥’")
  # =&gt; "\\"
  </code></pre>
  
  <p>Why is that, and how can I convert multi-byte characters?</p>
  
  <p>I am using Ruby 2.3.3. In addition, I get:</p>
  
  <pre><code>"\\".encoding #=&gt; #&lt;Encoding:UTF-8&gt;
  "\\¥'".encoding #=&gt; #&lt;Encoding:UTF-8&gt;
  "＼￥’".encoding #=&gt; #&lt;Encoding:UTF-8&gt;
  </code></pre>
  
  <p>Is this Ruby's bug?</p>