“We anticipate that this will be a significant challenge, both for insurers and for providers,” said Ceci Connolly, PwC's Health Research Institute's managing director. “Some large integrated health systems are already looking at specific geographic markets where this could be a problem and are working on translating material, bilingual call center staffers, bilingual signage, and multi-lingual providers.”

Avalere also estimates that nearly 12 percent, or about 960,000, of the new Medicaid enrollees will have a serious mental illness that requires treatment.

“You’ve got a disproportionately high prevalence of serious mental illness, schizophrenia, major depressive disorders, manic depression, which of course contributes to their not being able to maintain a job and have a higher income,” said Caroline Pearson, health reform director at Avalere.

But because they are younger than the current Medicaid population, the new enrollees also will be less likely to have the sorts of nagging, chronic illnesses that older Medicaid enrollees face. In fact, nearly four out of five new enrollees self-report their health condition to be either good, very good or excellent, according Avalere.

That bodes well for holding down the cost of their care. But until they are actually in the health care system, speculation about their medical needs is still a guessing game.

Assuming that newly insured people will take advantage of their coverage and discover undetected illnesses is a safe bet in the long run, but other experts say an initial spike in treatments might not occur as soon as expected.

“The picture is a bit more complicated because there’s other research that says when people gain coverage, it takes them a while to figure out how to use those new services,” said Matthew Buettgens, a senior research associate at the Urban Institute’s Health Policy Center. “So what happens in the initial months when they gain coverage is a bit uncertain.”

Most experts agree that having insurance and a primary caregiver increases the likelihood that the new enrollees’ health problems will be treated in a timely manner, which holds down the cost of care.

States originally were required to expand their Medicaid rolls under the Affordable Care Act or face the loss of federal funding. But that mandate was ruled unconstitutional by the U.S. Supreme Court in June 2012. In the aftermath of the decision, however, many Republican governors – including some who vowed to block the Medicaid expansion – have since come to support it.

Their about-face stems largely from the fact that the federal government will cover the cost of the newly eligible Medicaid recipients in 2014, 2015 and 2016. After that, the states’ share of the costs for these enrollees will gradually rise to 10 percent in 2020 and remain at that level thereafter.

The 8 million new Medicaid enrollees in 2014 likely will grow to 11 million in 2015 and 12 million by 2020, according to government estimates. This will strain Medicaid’s ability to provide care, since many doctors don’t accept Medicaid patients because the government pays less for their care than for Medicare patients.

The health care law increases doctors’ Medicaid reimbursement rates to the same level as Medicare in 2013 and 2014. But after that, Congress would have to increase the rates again – which is no sure bet – or face the very real possibility of doctors turning away millions of Medicaid patients in 2015.

Higher reimbursement rates would help ensure there are enough providers to care for the expanded Medicaid caseload in 2015 and thereafter, said Dr. Jeffrey Cain, president of the American Academy of Family Physicians.

“To expand Medicaid without having enough providers is like giving everyone a bus ticket to a city, but not providing any more buses,” Cain said.