how to make the change of vendor/elgg/elgg/mod/uservalidationbyemail/languages/ja.php effective

Hi, I am new to Elgg.

I installed elgg-3.3.17 and it seems working well with Japanese.

However, when a new user tried to create his account, he received a validation mail in English,
even though I setup the site default language as Japanese.

I found that vendor/elgg/elgg/mod/uservalidationbyemail/languages/ja.php contains English for that part.
So I changed the part into Japanese.

But still a new user receives the validation mail in English.
What should I do?