I want to combine Helvetica World (for roman, cyrillic, greek and arabic) and Hei Std (for simplified chinese) in one document with LuaLaTeX. Hei Std probably hasn't all the glyphs from Helvetica World and Helvetica World certainly hasn't all characters from Hei Std.
Can I get LuaLaTeX to automatically choose the right font based on the input, i.e. can I combine fonts into one "virtual font"? I don't want to switch the fonts manually.
Out of curiosity I'm also interested in a solution for XeLaTeX, but I need one for LuaLaTeX.