replying in other language in Apple Watch

I have a problem with my Apple Watch series 1 2nd edition.

When I got messages from other people, I only can reply in English. Even if I press the reply screen firmly and choose another language, the choices of language shows up on to the screen is still English.

The language I want to send is Japanese. The messages that I want to reply are also Japanese. I read that in order to use dictation in another language, I need to have that language's keyboard. So, I deleted every keyboard except Japanese one, still I only can reply in English.

In order to solve this problem, I restarted my Apple Watch and my iPhone, but it did not solve the problem.

My iPhone language and Watch language are both English. I changed to Japanese, though it did not solve the problem.

my Apple Watch series 1, 2nd edition. version is 4.3.2. I got this a week ago.

my iPhone X's version is 11.4.1.

please help me.