to extend he/she can smoothly communicate with natives and to extend he/she can get a job in that place?
clearly the answer is no.
even a native speaker doesn't become fluent in their own language, as a baby/child, in a few months, in full immersion from birth, so why a learner should become fluent in a few months???
it's not necessary to be fluent to find a job in the chosen country and to communicate with natives.
as adults, we probably would like to be "fluent" overnight because as long as we are not, we feel like children when we try to express our ideas and don't find our words and it's frustrating. it takes humility to learn a language, to learn anything.
In a "few" months, can you function and communicate with a sympathetic listener who doesn't mind hearing an accent, grammatical errors, and is willing to spend time speaking slowly, repeating, asking for repetitions, and clarifying meanings... maybe.
Can you achieve "fluency" in the sense of smooth flow, not halting, not searching for words... maybe.
Can you get a paying job in customer service job, talking on the telephone with native English speakers, and helping them understand complicated telephone plans, dealing with irritated customers whose orders have gotten mixed up... no.
Not likely anyway. I suppose there might be a few rare people with unusual natural talent who can do it.
In any case, I'd guess that a "few" months would be more like 8 than like 2.
2 of 2
Finally I don't particularly like that analogy that because babies and children take a long time to become fluent in their mother tongue an adult learner will too. For one, children at that age are not consciously trying to learn a new language, so an adult with the right learning strategy should be more effective at learning a foreign language.
Babies and children have brains that have not yet fully developed, but their brains are like 'sponges' with a high capacity to soak up new information which means they can pick up a language without consciously trying to. Adults do not have this ability but they have the intellectual capability to strategically plan and focus their learning in a way to achieve the best results.
Another very important point is that young children have not yet achieved fluency in any language. They have to learn how to do it all for the first time, which is why it takes a long time to achieve. An adult has already been through this process at least once (with their mother tongue), so with the right learning strategy it should take less time than a baby to learn another language.
Now of course there are many obstacles to achieving this goal, not least the amount of time you can commit to learning a foreign language and the fact it can be very hard to maintain your motivation. But as I said at the start, I think it is possible in some situations.