No, the unbeliever would be unconverted by tongues if he did not understand that particular tongue.
That is why a interpreter was necessary.
However, if an unbeliever came in when prophecy (for the purpose of edification) was going on, he would benefit from that.
Also, tongues were to be given in order, so the unbeliever would not consider the church in a state of confusion.
In conclusion, even when tongues was in operation it was considered the least of all the gifts.
Yes, the least, but even the least of the gifts from our loving God shouldn't be impuned.