Avoid a character set in the meta tag AND Specify a character set
I have alredy add code in my php web page like...
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
than after in https://developers.google.com/speed suggest for
- Specify a character set
- Avoid a character set in the meta tag
Answer
Use a HTTP header rather than a meta tag. Implementing that depends on what server-side tech you are using.
If you are generating your content using PHP, put this at the top of your page:
header("Content-Type: text/html; charset=utf-8");
If you are using any other server-side programming language, there must be a similar option.
Alternatively, if you are using Apache, you can do it using htaccess directives as follows:
AddType 'text/html; charset=UTF-8' html
And if you're using nginx, put this in your config:
more_set_headers -t 'text/html' 'Content-Type: text/html; charset=utf-8';
More on the meta tag "avoidance"
Google dev tools suggest removing meta tags wherever possible due to the information duplication that it may cause. Some webservers automatically send content-type headers, for example, and in some cases, incoherent meta tags can cause browsers to get... shall we say, confused.
To avoid duplication of information and possible charset-related headaches, always prefer headers over meta tags.