How to fix bugs in Morse alphabet code?

[Axel_Erfurt]

import string

alphabet = {}
morse = {}


translation_dict = dict([('a', '.-'), ('b', '-...'), ('c', '-.-.'), ('d', '-..'), ('e', '.'), ('f', '..-.'), ('g', '--.'), ('h', '....'), ('i', '..'), ('j', '.---'), ('k', '-.-'), ('l', '.-..'), ('m', '--'), ('n', '-.'), ('o', '---'), ('p', '.--.'), ('q', '--.-'), ('r', '.-.'), ('s', '...'), ('t','-'),('u', '..-'), ('v', '...-'), ('w', '.--'), ('x', '-..-'), ('y', '-.--'), ('z', '--..'), (' ', ''), ('/', '-..-.'), ('-', '-....-'), ('.', '.-.-.-'), (',', '--..--'), (' ', ''), ("1", ".----"), ("2", "..---"), ("3", "...--"), ("4", "....-"), ("5", "....."), ("6", "-...."), ("7", "--..."), ("8", "---.."), ("9", "----."), ("0", "-----")])



for key, value in translation_dict.items():
    alphabet[key] = key
    alphabet[value] = value

def encode(plaintext):
    morse_text = ""
    plaintext = plaintext.lower()
    for char in plaintext:
        morse_text += alphabet[char] + "/"
    morse_text += "//"
    return morse_text

def decode(mroz_text):
    plain_text = ""
    morse_array = mroz_text.split("/")
    for val in morse_array:
        plain_text += val
    return plain_text


print(encode("This is first testing sentence.")) # for testing
print(decode(encode("This is first testing sentence.")))
print(decode(encode("This is second testing sentence.")))
print(decode(encode("This is third testing sentence.")))
print(encode("ka b")) # -.-/.-//-...///

Output:
t/h/i/s/ /i/s/ /f/i/r/s/t/ /t/e/s/t/i/n/g/ /s/e/n/t/e/n/c/e/.///
this is first testing sentence.
this is second testing sentence.
this is third testing sentence.
k/a/ /b///