Question

For example:

local a = "Lua"
local u = "Луа"
print(a:len(), u:len())

output:

3   6

How can I output number of characters in utf-8 string?

Answer 1

If you need to use Unicode/UTF-8 in Lua, you need to use external libraries, because Lua only works with 8-bit strings. One such library is slnunicode. Example code how to calculate the length of your string:

local unicode = require "unicode"
local utf8 = unicode.utf8

local a = "Lua"
local u = "Луа"
print(utf8.len(a), utf8.len(u)) --> 3    3