Tags with diacritical marks issue

[partyzant]

I can't add tags to post with diacritical marks (for example polish word "bąk") and then the same word without diacritical marks "bak" from edit post panel, because function term_exists() in wp-includes\taxonomy.php returns true when checking if this tag already exists. I can do this from tag edit panel, but this is more time concuming.