How to deal with Opera glitch in Open Sans?

Question

Opera

If you set font-weight: bold; and Open Sans to Russian text (i.e. Cyrillic), then Opera will have squares instead of Russian letters. How can this be dealt with?
(use a different font or not bold - extreme measures)

Answer 1

Almost figured it out, but still need help. The problem was that the Cyrillic subset was not connected. Here is what I found in /wp-includes/script-loader.php:

/* translators: To add an additional Open Sans character subset specific to your language,
             * translate this to 'greek', 'cyrillic' or 'vietnamese'. Do not translate into your own language.
             */
            $subset = _x( 'no-subset', 'Open Sans font: add new subset (greek, cyrillic, vietnamese)' );

            if ( 'cyrillic' == $subset ) {
                    $subsets .= ',cyrillic,cyrillic-ext';
            } elseif ( 'greek' == $subset ) {
                    $subsets .= ',greek,greek-ext';
            } elseif ( 'vietnamese' == $subset ) {
                    $subsets .= ',vietnamese';
            }

            // Hotlink Open Sans, for now
            $open_sans_font_url = "//fonts.googleapis.com/css?family=Open+Sans:300italic,400italic,600italic,300,400,600&subset=$subsets";
    }

If you change no-subset to cyrillic in the code, then everything is ok. But I don’t want to change the code so that it doesn’t crash when updating WP. In translation, too, since again it will crash when updating WP.
How to make "human"?

Answer 2

Maybe Opera can't just emulate Cyrillic boldface. Bold will require a separate Open Sans Bold headset,