The character (ể) is unicode codepoint U+1EC3, which is not part of WIN1258, and therefor won't be stored (or displayed) using WIN1258. Make sure you use UTF8 for both your connection characterset, database/column characterset and that the application, console or whatever you use for display also supports this character.
See also http://www.scarfboy.com/coding/unicode-tool?s=U%2B1ec3