Hydrangea is a symbolic flower of Nagasaki, Japan.
According to the website below, there are several languages of this flower.
https://thesecretlanguageofflowers.wordpress.com/tag/hydrangea-meaning-in-the-language-of-flowers/
Heartfelt and honest emotions of any kind
Gratitude and thanksgiving to someone else
Developing a deeper understanding between two people
Heartlessness and acting without thinking about the feelings of another
Frigidity and disinterest in a romantic proposal
Boasting and bragging about false accomplishments
Abundance and prosperity
Grace and beauty, sometimes taken to an extreme of vanity and narcissism
the 4th wedding anniversary for a couple