The plain utf8 covers the "basic multilingual plane" (x0000-xFFFF), so it will get you very far, actually.
In our app, we finally went for utf8mb4 to allow people to enter emoji. As a side "bonus" you will also soon see some clever people entering their names to stand out, such as "πΉπππ". Note that this is not "John". It is actually a series of mathematical symbols:
U+1D679 MATHEMATICAL MONOSPACE CAPITAL J
U+1D698 MATHEMATICAL MONOSPACE SMALL O
U+1D691 MATHEMATICAL MONOSPACE SMALL H
U+1D697 MATHEMATICAL MONOSPACE SMALL N
In our app, we finally went for utf8mb4 to allow people to enter emoji. As a side "bonus" you will also soon see some clever people entering their names to stand out, such as "πΉπππ". Note that this is not "John". It is actually a series of mathematical symbols: