Glitch text is text generated on the fly in-game, used starting in Act 2. It usually is generated at a set length for each situation it's called, with the exception of the end of Act 2 while the player stays with Yuri's corpse.
To generate glitch text, the game simply chooses random characters from the following pool of characters:
¡¢£¤¥¦§¨©ª«¬®¯°±²³´µ¶·¸¹º»¼½¾¿ÀÁ ÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàá âãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿĀā ĂăĄąĆćĈĉĊċČčĎďĐđĒēĔĕĖėĘęĚěĜĝĞğĠġ ĢģĤĥĦħĨĩĪīĬĭĮįİıĲĳĴĵĶķĸĹĺĻļĽľĿŀŁ łŃńŅņŇňŉŊŋŌōŎŏŐőŒœŔŕŖŗŘřŚśŜŝŞşŠš ŢţŤťŦŧŨũŪūŬŭŮůŰűŲųŴŵŶŷŸŹźŻżŽž
Many of these characters don't have glyphs in the font used to render text in-game, and as such will appear as rectangles. Generated glitch text is also often paired with the edited style.