Google builds a beautiful font (Noto) for the world. How can I replace the system default font with the Noto font?
As Per this site
Install gujarati fonts in Android
Google has finally added Gujarati fonts to Android 5.0 (Lollipop) in the Nexus line of phones. The fonts are called Noto Sans Gujarati and Noto Sans Gujarati UI and both come in regular and bold versions, though they are seemingly indistinguishable. Google still has to add Gujarati keyboard input though so we can type in Gujarati. Until then, SwiftKey Keyboard is currently offering a Gujarati input method. Images below show the Noto Sans Gujarati font displayed natively on my website. The third image shows the SwiftKey keyboar layout for Gujarati input.
Note : you have to root your android device and it voids warranty from manufacturer