The “boxes” are a result of the default font style within the titles not supporting the characters of the inputted language. In the above example image, the font style Arial was listed as the default. However, the Arial font style does not support the inserted characters.
Once you’ve selected a title and come across the “boxes” when typing in your language of choice, it is recommended that you switch to a font style that supports that language.
Here is a list of fonts that most commonly support multiple languages for iOS and Android Rush users. Your supported fonts may vary based on the device.