diff --git a/README.md b/README.md
index 5a84bd3..17c7760 100644
--- a/README.md
+++ b/README.md
@@ -71,6 +71,7 @@ Commands
 | unko.king     | Build your king shift tower. |
 | unko.fizzbuzz | No need to implement FizzBuzz. |
 | unko.ping     | Ping the 💩 domain. |
+| unko.encode   | Encode/Decode data and print to standard output. |
 | unko.date     | TBD |
 | unko.awk      | TBD |
 | unko.xargs    | TBD |
diff --git a/bin/unko.encode b/bin/unko.encode
index d3e2e35..45f5796 100755
--- a/bin/unko.encode
+++ b/bin/unko.encode
@@ -1,7 +1,13 @@
 #!/bin/bash
 
-UNKO_OCT=(う ん こ ウ ン コ 💩 👑)
+if [[ "$LANG" = zh* ]] || [[ "$LANG" = en* ]]; then
+  export TEXTDOMAINDIR="/usr/share/locale-langpack/${LANG%%.*}/LC_MESSAGES"
+else
+  export TEXTDOMAINDIR="/usr/share/locale-langpack/${LANG%%_*}/LC_MESSAGES"
+fi
+export TEXTDOMAIN=libc
 
+UNKO_OCT="うんこウンコ💩👑"
 usage() {
   echo "Usage: $0 [OPTION] [FILE]"
   echo "Unko encode or decode FILE, or standard input to standard output."
@@ -11,38 +17,30 @@ usage() {
 }
 
 encode() {
-  od -b -v -An "$1" |
-    tr -d ' \n' |
-    sed "
-    s/0/${UNKO_OCT[0x0]}/g;
-    s/1/${UNKO_OCT[0x1]}/g;
-    s/2/${UNKO_OCT[0x2]}/g;
-    s/3/${UNKO_OCT[0x3]}/g;
-    s/4/${UNKO_OCT[0x4]}/g;
-    s/5/${UNKO_OCT[0x5]}/g;
-    s/6/${UNKO_OCT[0x6]}/g;
-    s/7/${UNKO_OCT[0x7]}/g"
+  od -b -v -An |
+    sed -e "y/01234567/$UNKO_OCT/" |
+    tr -d ' \n'
   echo
 }
 
 decode() {
-  sed "s/[^うんこウンコ💩👑]//g" "$1" |
-    tr -d '\n' |
-    sed "
-    s/${UNKO_OCT[0x0]}/0/g;
-    s/${UNKO_OCT[0x1]}/1/g;
-    s/${UNKO_OCT[0x2]}/2/g;
-    s/${UNKO_OCT[0x3]}/3/g;
-    s/${UNKO_OCT[0x4]}/4/g;
-    s/${UNKO_OCT[0x5]}/5/g;
-    s/${UNKO_OCT[0x6]}/6/g;
-    s/${UNKO_OCT[0x7]}/7/g" |
-    sed 's/.../0& /g' |
-    xargs printf %02x |
-    xxd -p -r
+  printf '%b' "$(
+    sed "s/[^$UNKO_OCT]//g" |
+      sed \
+        -e "s/${UNKO_OCT:0:1}/0/g" \
+        -e "s/${UNKO_OCT:1:1}/1/g" \
+        -e "s/${UNKO_OCT:2:1}/2/g" \
+        -e "s/${UNKO_OCT:3:1}/3/g" \
+        -e "s/${UNKO_OCT:4:1}/4/g" \
+        -e "s/${UNKO_OCT:5:1}/5/g" \
+        -e "s/${UNKO_OCT:6:1}/6/g" \
+        -e "s/${UNKO_OCT:7:1}/7/g" |
+      tr -d '\n' |
+      sed 's/.../\\&/g'
+  )"
 }
 
-MODE="ENCODE"
+EXEC_COMMAND="encode"
 FILE="-"
 
 for arg in "$@"; do
@@ -51,15 +49,23 @@ for arg in "$@"; do
       usage
       exit 0
       ;;
-    "-d" | "--decode") MODE="DECODE" ;;
+    "-d" | "--decode") EXEC_COMMAND="decode" ;;
     *) FILE="$arg" ;;
   esac
 done
 
-if [ "$MODE" = "DECODE" ]; then
-  decode "$FILE"
+if [ "$FILE" = - ]; then
+  "$EXEC_COMMAND"
 else
-  encode "$FILE"
+  if [ -f "$FILE" ]; then
+    "$EXEC_COMMAND" < "$FILE"
+  elif [ -d "$FILE" ]; then
+    printf '%s: %s: %s\n' "$0" "$FILE" $"Is a directory" >&2
+    exit 1
+  elif ! [ -e "$FILE" ]; then
+    printf '%s: %s: %s\n' "$0" "$FILE" $"No such file or directory" >&2
+    exit 1
+  fi
 fi
 
 exit 0
diff --git a/docker/Dockerfile b/docker/Dockerfile
index d22865b..85c8109 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -15,6 +15,7 @@ RUN echo -e $'\n\
 ENV LANG ja_JP.UTF-8
 RUN apt update -yqq \
     && apt install -y --no-install-recommends \
+       language-pack-ja-base \
        toilet \
        figlet \
        bc \
diff --git a/test/unko.encode-test.bats b/test/unko.encode-test.bats
new file mode 100755
index 0000000..c683ab8
--- /dev/null
+++ b/test/unko.encode-test.bats
@@ -0,0 +1,80 @@
+#!/usr/bin/env bats
+source functions.sh
+
+readonly TARGET_COMMAND="../bin/unko.encode"
+
+@test "-h でヘルプを出力する" {
+  run "$TARGET_COMMAND" -h
+  echo "$output"
+  [ "$status" -eq 0 ]
+  [[ "${lines[0]}" =~ ^Usage:.* ]]
+  coverage "$TARGET_COMMAND" -h
+}
+
+@test "--help でヘルプを出力する" {
+  run "$TARGET_COMMAND" --help
+  echo "$output"
+  [ "$status" -eq 0 ]
+  [[ "${lines[0]}" =~ ^Usage:.* ]]
+  coverage "$TARGET_COMMAND" --help
+}
+
+@test '引数なしのときは標準入力をエンコード' {
+  run "$TARGET_COMMAND" <<< うんこ
+  echo "$output"
+  [ "$status" -eq 0 ]
+  [ "${lines[0]}" = "ウンウこうんこう💩ウンウこうこここウウンウこうんここウうんこ" ]
+  coverage "$TARGET_COMMAND" <<< うんこ
+}
+
+@test '-d で標準入力をデコード {
+  run "$TARGET_COMMAND" -d <<< ウンウこうんこう💩ウンウこうこここウウンウこうんここウうんこ
+  echo "$output"
+  [ "$status" -eq 0 ]
+  [ "${lines[0]}" = "うんこ" ]
+  coverage "$TARGET_COMMAND" -d <<< ウンウこうんこう💩ウンウこうこここウウンウこうんここウうんこ
+}
+
+@test '--decode で標準入力をデコード {
+  run "$TARGET_COMMAND" --decode <<< ウンウこうんこう💩ウンウこうこここウウンウこうんここウうんこ
+  echo "$output"
+  [ "$status" -eq 0 ]
+  [ "${lines[0]}" = "うんこ" ]
+  coverage "$TARGET_COMMAND" --decode <<< ウンウこうんこう💩ウンウこうこここウウンウこうんここウうんこ
+}
+
+@test 'ファイルが存在しない場合エラー' {
+  export LANG=ja_JP.UTF-8
+  run "$TARGET_COMMAND" うんこ
+  echo "$output"
+  [ "$status" -eq 1 ]
+  [[ "${lines[0]}" =~ .*そのようなファイルやディレクトリはありません ]]
+  coverage LANG=ja_JP.UTF-8 "$TARGET_COMMAND" うんこ
+}
+
+@test 'ディレクトリの場合エラー' {
+  export LANG=ja_JP.UTF-8
+  run "$TARGET_COMMAND" .
+  echo "$output"
+  [ "$status" -eq 1 ]
+  [[ "${lines[0]}" =~ .*ディレクトリです ]]
+  coverage LANG=ja_JP.UTF-8 "$TARGET_COMMAND" .
+}
+
+@test 'ファイルが存在しない場合エラー(英語版)' {
+  export LANG=en_US.UTF-8
+  run "$TARGET_COMMAND" うんこ
+  echo "$output"
+  [ "$status" -eq 1 ]
+  [[ "${lines[0]}" =~ .*"No such file or directory" ]]
+  coverage LANG=en_US.UTF-8 "$TARGET_COMMAND" うんこ
+}
+
+@test 'ディレクトリの場合エラー(英語版)' {
+  export LANG=en_US.UTF-8
+  run "$TARGET_COMMAND" .
+  echo "$output"
+  [ "$status" -eq 1 ]
+  [[ "${lines[0]}" =~ .*"Is a directory" ]]
+  coverage LANG=en_US.UTF-8 "$TARGET_COMMAND" .
+}