Is there a word in English for the inability to utter a specific sound like the rolled R for instance? In my language, there is a name for people who can only pronounce the uvular/guttural R instead of the rolled R. I'm curious to know if there is a word in English for this condition.
There is the term Rhotacism
which relates to the difficulty in producing what many would consider to be a 'typical' /r/.
In general, the inability to pronounce a particular sound (that everyone else in the community can) is called a
This is more likely to describe a lisp or stammer or more serious inability arising from a physical disability or neurological problem.
If the word you're looking for should literally mean "unable to pronounce a rolled R," then Guarin42's answer looks great.
On the other hand, if the connotation is "this person can't pronounce a certain sound, indicating that they come from a certain group," then you could say that the word or sound they can't pronounce would be a shibboleth. This word specifically refers to a word or phrase that members of one group pronounce differently than members of another group, allowing people to identify to which group everyone belongs.
Hope this helps!