The downside to switching languages if they child is going to do year 2, then they will need to do at least 2 of the new language where in some cases they could stop (if they chose) after year 2 on the original one. That can become more of a scheduling question than anything. If the student takes year 2 in 9th and year 3 in 10th, then the language slot opens up for other classes in 11th. If the student wants 3 years of language for the more competitive schools, and switches language, in theory they only open up a “slot” in 12th grade.
I would weigh all and also see what it was my student really wanted. At the end of the day, I let them make the call.