Do all character entities display properly on all systems?

Answer 1

No. It depends on whether or not the right fonts are available on the system. Now many programs like browsers use fall back fonts. I.e. if a font is not available the program displays the characters in a different font. This is usually not a problem as long as the characters belong to the same alphabet. But if you use an alphabet for which there is no fall back available on the system or if you use special symbols like emojis this can fail. In that case it can happen that the wrong symbol is displayed or that the symbol is replaced by a placeholder like a box with a question mark in it.

Answer 2

Thanks