Many colleges are fine with just two years of foreign language (and some don't demand any foreign language at all). But the more selective colleges and universities typically expect three years of the same foreign language (and may even prefer four). So by stopping Spanish at the end of 10th grade, you will definitely limit your college options down the road. Although admission officials might look the other way if you apply with fewer than the expected years of foreign language, you will be “competing" with other applicants who have fulfilled this requirement so—unless you have clear-cut strengths that make up for this deficiency—the lack of language classes will be a liability.
Individual college Web sites will tell you what the language requirements are for admission, so if you already have specific schools in mind, you can look them up now. College Confidential's SuperMatch can also help you compare language requirements at the places you are considering.
First go to: http://www.collegeconfidential.com/college_search/
Next, type in the name of the college that interests you on the upper left hand side of the page where it says, “"Enter name of school."
Then, go to that college's page and click on the “School Facts" tab.
Finally, click on the “Admissions" icon to see a list of “High School Prerequisites."
For Foreign Language, it's common to see a difference between the “Years Required" figure and the “Years Recommended" figure. Obviously, if your curriculum meshes with the Recommendations rather than the Requirements, you will be in a stronger position. AP Language classes (and exams) are never imperative. However, admission folks do like to see that students have challenged themselves in as many academic areas as possible. So if you like Spanish and do well in it, it certainly makes sense to continue it through the AP level. But if you're not so keen on it or simply want to make room for other classes, it's certainly not imperative that you pursue Spanish through AP.
If you're eager to take extra science classes that won't fit into your schedule due to Spanish, consider finding courses at a local community college or through a summer program. While some of the latter can be pricey, if you do a Google search for “Summer Science Programs for High School Students," you may find a lot of options. And if you add the name of your city or town to your search, you could turn up some local options that are affordable for most families or even free. The fact that you went out of your way to study science in the summer should be at least a small plus at admission decision time as well, and it won't get in the way of your continuing with Spanish.