The Roboto font doesn't support all languages. The Noto font should be used for languages that Roboto doesn't support, including Chinese (simplified and traditional), Japanese, Korean, Thai and Hindi (https://en.wikipedia.org/wiki/Roboto#Language_coverage).

Right now, qquickmaterialtheme only falls back to Noto if Roboto cannot be found (http://code.qt.io/cgit/qt/qtquickcontrols2.git/tree/src/imports/controls/material/qquickmaterialtheme.cpp#n48). However, it should also fallback to Noto if the language is not supported.