HTML Guide for utf-8

In order to define the charset encoding of an HTML document, both of these options are valid, but only one of them must appear in the document:

<!-- This is the preferred way -->
<meta charset="UTF-8">

<!-- This is the older way, also valid -->
<meta http-equiv="content-type" content="text/html; charset=UTF-8">

A <meta> tag has been found in the document stating that the charset is windows-1251, but it actually is utf-8. You should update the tag to reflect the actual encoding of the document, for example:

<meta http-equiv="Content-Type" content="text/html; charset=utf-8">

A <meta> tag has been found in the document stating that the charset is windows-1252, but it actually is utf-8. You should update the tag to reflect the actual encoding of the document, for example:

<meta http-equiv="Content-Type" content="text/html; charset=utf-8">

A character has been found in the document that is not allowed in the charset encoding being used.

The document has been declared to use a windows-1251 charset but the actual contents seems to be utf-8. You should update the charset to that like in this example:

<meta http-equiv="Content-Type" content="text/html; charset=utf-8">

In HTML5 you’re encouraged to use Unicode (UTF-8) character encoding rather than a legacy character encoding such as Latin1 (Windows-1252 or ISO 8859-1).

In short, it can be just a matter of using <meta charset="utf-8"/> in your document, but you should also ensure that your pages are also saved and served as UTF-8.