When I lived in LOS, I knew a number of foreigners who described themselves as 'fluent'. When they spoke, Thai just gawped at them - no idea what they were trying to say. I lived in LOS for six years - three in Aranyaphathet, where almost no English was spoken. On my most linguistically fluent day, I would have called myself a novice. I had some friends who spoke very good Thai, but only one would have really been considered fluent, and he had studied Thai for years, and lived in the country for decades - in fact, he is buried in Chiang Mai.