Can I apply for a Thai DTV visa from a different country than where I currently am?

No

But why you won’t apply from Japan if you there?

Nope you need entry stamp evidence

You've been in this group for almost a month and you really felt you needed to ask this question?

Don't do it and don't leave until it's approved.

The only thing the Thailand e-visa system does is change the method of sending in your information. It's still processed by the local Thai embassy or consulate based on where you are. The embassy can and has asked for proof you are in the country like passport pages and proof of fully paid hotel bookings. They can also ask people to come in for interviews. There is also this little note under current location "Your current location is a country or territory in which you remain at the time that you lodge an application" that everyone seems to ignore.

NOPE 👎

NOOOOOO

No, you can't. You need to apply where you are. You'll be requested proves of location. And the same applies after having provided the first documents as additional proves of location may be requested.