How important is it to continue to take foreign language in HS after finishing requirement?

Yes. AP scores are self reported. An official score report only needs to be sent to the school one is attending for credit/placement. Sending official AP score reports with applications is a waste of money.

As far as the scores themselves, well, a wall of 5’s will be viewed more favorably than a mix of 2’s and 3’s, but IMO 13 4’s and 5’s is not more impressive to admissions than 5 4’s and 5’s. School differ on AP policies, course restrictions, offerings, etc. And then there is the socioeconomic conversation regarding cost.