During basic you'll have to take the DLAB (Defense Language Aptitude Battery), and scoring high on the test will likely get you assigned a strategic language. However, if you are already very good at a language and decide to take the placement test for that language, and is able to validate at least one semester, then you can pretty much be guaranteed to be placed in that language. The DLAB doesn't hold much weight if you take any language validation tests.
That being said I've never heard of anyone not taking a foreign language at all (with the exception of exchange and international cadets), just people validating into higher level classes.