• Go

slices.SortFunc(data, func(a, b string) int {
	return cmp.Compare(strings.ToLower(a), strings.ToLower(b))
})

• Go

sort.Slice(data, func(i, j int) bool {
	return strings.ToLower(data[i]) < strings.ToLower(data[j])
})

• Go

func lessCaseInsensitive(s, t string) bool {
	for {
		if len(t) == 0 {
			return false
		}
		if len(s) == 0 {
			return true
		}
		c, sizec := utf8.DecodeRuneInString(s)
		d, sized := utf8.DecodeRuneInString(t)

		lowerc := unicode.ToLower(c)
		lowerd := unicode.ToLower(d)

		if lowerc < lowerd {
			return true
		}
		if lowerc > lowerd {
			return false
		}

		s = s[sizec:]
		t = t[sized:]
	}
}

sort.Slice(data, func(i, j int) bool { return lessCaseInsensitive(data[i], data[j]) })

• Dart

data.sort((a, b) => a.toUpperCase().compareTo(b.toUpperCase()));

• Java

data.sort(String::compareToIgnoreCase);

• Pascal

data.sort;

• Perl

@data = sort { lc($a) cmp lc($b) } @data;

• Python

data.sort(key=str.lower)

• Ruby

data.sort_by!(&:downcase)

• Rust

data.sort_by_key(|k|k.to_lowercase());