I’d like to create my own keyboard with mini led matrixes on keykaps.

5x7 indicator would be fine for that, it can display almost all cyrillic letters and all latin.

It’s size is 12.7mm x 17.8 mm. This is slightly bigger that 1.5mm that is standard key size, but that’s the only available option.

It would be quite difficult and expensive to design PCB with 5x9 0201 LEDs (0.65x0.35mm - the tiniest LED available on market).
Maybe it is worth considering bigger resolution with 0201 LEDS for chinese font.

Here is the font example:

HD44780 character table with cyrrilic:

And for chinese/japanese/korean/thai/etc characters 11x11 px should be enough:

https://github.com/SolidZORO/zpix-pixel-font