fix: parse single-rune Unicode flags

command_parse.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"strings"
 	"unicode"
+	"unicode/utf8"
 )
 
 const (
@@ -133,7 +134,7 @@ func (cmd *Command) parseFlags(args Args) (Args, error) {
 		if firstArg[1] == '-' {
 			numMinuses++
 			shortOptionHandling = false
-		} else if !unicode.IsLetter(rune(firstArg[1])) {
+		} else if firstRune, _ := utf8.DecodeRuneInString(firstArg[1:]); !unicode.IsLetter(firstRune) {
 			// this is not a flag
 			tracef("parseFlags not a unicode letter. Stop parsing")
 			posArgs = append(posArgs, rargs...)

command_test.go

@@ -1229,6 +1229,27 @@ func TestCommand_FlagValuesKeepWhitespace(t *testing.T) {
 	}
 }
 
+func TestCommand_SingleRuneUnicodeFlag(t *testing.T) {
+	const name = "ש"
+	assert.Equal(t, "-", prefixFor(name))
+
+	var value string
+	var args []string
+	cmd := &Command{
+		Name:  "app",
+		Flags: []Flag{&StringFlag{Name: name}},
+		Action: func(_ context.Context, cmd *Command) error {
+			value = cmd.String(name)
+			args = cmd.Args().Slice()
+			return nil
+		},
+	}
+
+	require.NoError(t, cmd.Run(buildTestContext(t), []string{"app", "-" + name, "value", "operand"}))
+	assert.Equal(t, "value", value)
+	assert.Equal(t, []string{"operand"}, args)
+}
+
 func TestCommand_EqualsFlagValueValidation(t *testing.T) {
 	for _, kind := range []string{"int", "bool"} {
 		for _, whitespace := range []string{"", " ", "\t"} {

docs.go

@@ -5,10 +5,11 @@ import (
 	"os"
 	"runtime"
 	"strings"
+	"unicode/utf8"
 )
 
 func prefixFor(name string) (prefix string) {
-	if len(name) == 1 {
+	if utf8.RuneCountInString(name) == 1 {
 		prefix = "-"
 	} else {
 		prefix = "--"