Translation tr() not returning translated word?

I imported a Translations.csv which contains

,en,ja
KEY_HELLO,Hello,こんにちは

Then I see these files were generated in res://
Translations.en.translation
Translations.ja.translation

Then I added Translations.en.translation and Translations.ja.translation to Project -> Project Settings -> Localization -> Translations.

I try to get the translated text for japanese locale in my scene with below code but it returns english

func _init():
	TranslationServer.set_locale("ja")
func _ready():
	var Locale = TranslationServer.get_locale() # this return ja
	var Test = tr("Hello") # this return Hello which is wrong