Per post/page custom values

Hi everybody,

Is there a way to set a custom value or variable (or whatever it’s called) per page and post? I’m thinking of a plugin that will add a table to UI where one would set variable’s name and valuation on each editing site.

Then in php source it would be referenced somehow like wp_title(); or $var. This way I could add a specific a href link to the header part which is common for all pages and posts. I need this to manage links between language versions of my sites and possibly to add some page-unique meta tags.

Or is there any other solution beside plugin? Searched a lot but without success. Sorry whether I’m asking about obvious.

Thank You Kindly.