Are you saying it takes a year and a half to reach fluency if you take it on as a full time job?
It's an organized class for 5 hours a day in small groups with a native speaker as the teacher.
There is usually an additional 2-5 hours of independent study/homework depending on the complexity of the language.
Professional fluency takes between 24 and 88 weeks depending on the difficulty of the language. Spanish is 24, Mandarin would be 88. "Hard" languages like Finnish and Estonian are in the middle at 44.
We test with native speakers at the end to determine our level on a 5 point scale. Each of our embassy jobs has an associated language requirement, usually 3/3, which means professionally fluent in speaking and reading.