YOU SAID:

this is a letter that will be explaining something that i have been keeping to myself for years.

INTO JAPANESE

これは私が何年も自分自身に保管してきたことを説明する手紙です。

BACK INTO ENGLISH

This is a letter explaining that I have kept it for myself for many years.

INTO JAPANESE

これは私が長年それを自分のために保管してきたことを説明する手紙です。

BACK INTO ENGLISH

This is a letter explaining that I have kept it for myself for many years.