A work on user-oriented Bengali orthography has been carried out while teaching Bengali as a Third language. Learning Bengali is difficult because of the presence of innumerable conjunct letters and the absence of a vowel-sign for the first vowel in Bengali orthography. It is extra difficult for foreigners because the working memory in learning a foreign language is quite limited. It is easy to make a computer-key-board with a thousand letters and signs, but it is difficult to use in practice. It is shown in this work that the Bengali conjunct letters not used as initial letters in word-making were redundant in its orthography and could be dissected to their components, if a missing-letter sign for the unborn first Bengali vowel-sign was raised in accordance with Bengali orthographic rule. Only 30 conjunct letters used in Bengali as initial letters in word-making which could be kept intact. Thus only 108 signs on a key-board, including 10 digits and 20 punctuation and other signs were sufficient in case of a user-oriented Bengali orthography.