Translation guide
The English phrase "not to mention ..." is used to add a stronger or more obvious point to an argument. In Japanese, this is expressed through various conjunctions and sentence-ending patterns that emphasize the addition of an even more significant item.
To introduce an additional, often more extreme or obvious, piece of information that reinforces the previous statement.
A common pattern meaning 'not only A but also B', where B is often more surprising or significant. It can be used to translate 'not to mention' when adding information.
He can speak English, not to mention Chinese.
Used to say 'far from A, even B', often implying that B is more extreme. It can convey the idea of 'not to mention' when emphasizing that even a more difficult or surprising thing is true.
He can't even walk, not to mention run.
Literally 'it goes without saying', this phrase can be used to introduce something that is obvious and doesn't need to be mentioned, similar to 'not to mention' in some contexts.
An adverb meaning 'much less' or 'let alone', used to emphasize that if something is true for a lesser case, it is even more true for a greater case. Often used in negative sentences.
A formal pattern meaning 'let alone A, even B'. It is used to emphasize that something is so extreme that even a lesser thing is not possible or true.
～はもちろん is used to add information in a neutral or positive way, while ～どころか often implies a contrast or that the second item is more extreme than expected. ～どころか can also be used in negative contexts to mean 'far from'.
He can speak Japanese, not to mention Korean.
Not to mention, health is important.
彼は簡単な料理も作れない。ましてやフルコースなんて無理だ。
He can't even cook a simple meal, not to mention a full-course dinner.
He has never traveled abroad, not to mention domestically.
He can't even speak English, not to mention Japanese.
Do not translate 'not to mention' literally as ～を言うまでもなく or similar in every case. The natural Japanese expression depends on the context and the relationship between the two items being compared.