Despite it being a Japanese word, I noticed both I and my friend were totally ok to understand it. In Chinese, "前略" can be broken down into "前" front and "略" omit, which means omit the front part of opening the letter.
However, another Japanese word used in letter is "不一", which means "Very sincerely yours (valediction in correspondence)" in Japanese, but means "varying; differing; different; not uniform" in Chinese.
I wonder what happened in the history to make the word have such a big difference in meaning.