"In Japan, English is already mandatory, yet, English fluency sucks."

Spoken fluency sucks. Reading and writing English is much better.

When I lived in Japan, and eventually achieved some basic fluency in speaking Japanese, communicating with my coworkers often consisted of English vocabulary, in sentences using Japanese pronunciation and grammar.

The reason for this is simple. They had plenty of access to English written material, and needed to read and understand it in order to do their job (computer science research).

But they had very little interaction with native English speakers on a day to day basis, so few opportunities to practice real time conversation. Which is the only way I know to actually become fluent speaking a second language.