YOU SAID:
Yesterday was the day when my future sister in law was celebrating her past 38 years of living
INTO JAPANESE
昨日は義理の妹が38歳を迎えた日でした
BACK INTO ENGLISH
Yesterday was the day my sister-in-law turned 38.
INTO JAPANESE
昨日は義姉が38歳になった日でした。
BACK INTO ENGLISH
Yesterday was the day my sister-in-law turned 38.
You should move to Japan!