Absolutely get evaluated. I spoke 3 languages and had speech therapy (for a lisp) that was not related to the language. Same for my son, who speaks 2 languages and had not only a lisp but also r/l issues. Neither was strong but since I knew what to look for we had him in speech therapy before teachers even suggested it--and I remember how carefully and almost timidly they broached the subject, a lot of parents must fly off the handle at the suggestion. He was already in therapy by the time they mentioned it. Took about a year or maybe a bit longer--hard to remember, he graduates from college next week.
I'm often shocked at the parents/kids who have a clear lisp that was never treated, because it's cute when they're little and often because parents think the kids will outgrow it. They don't.