Oh good! That means they don't have both T and D, or both P and B, or both K and G.The thing is, the Polynesian languages mentioned above (at least for the most part, I cannot vouch for all of them) have none of those distinctions.
There is also a phonetic problem between the new language and the learner's native language. How difficult is it for them to hear and speak sounds that don't exist in their native language? But that isn't avoidable, and only means it will be harder for some people to learn than for others.