Among "non-photographers" in English speaking countries, I would think that "lens" would be much more understandable than "objective". Pretty much anyone who understands the technical meaning of "objective" used in the context of an optical system would also understand what "lens" means. The obverse would not be the same case, not everyone who understands what a "lens" is would also understand what "objective" means when used in the same context. There are many English speaking photographers who have not a clue where their camera's "objective" is located. They all know what "the lens" is.
As someone who is an English speaker and has been doing photography for almost 50 years, I'd say that a compound lens system is usually called a "lens" when used in the context of creative photography, which is what Photography.SE is mostly about. We even call catadioptric mirror + lens systems used on cameras "mirror lenses."
Back in the late 20th century among photographers, at least in the U.S., "objective" tended to refer to the first lens element or group of elements in a compound lens system. For example, with a 70-200mm f/2.8 lens with 23 elements in 19 groups, the first 2 lens elements would be considered the "objective group".
Though it is true that in the nomenclature of optical physics, lens refers to a single optical element, in the nomenclature of cameras, "lens" can and does often refer to the entire light gathering optical system made up of many lens elements and even mirrors.
Based on one quarter (as opposed to semester - if that doesn't date me as a fossil nothing does) of 'German Language and Culture' back in my college days, I'd say that the way most German speakers use das objektiv is very similar to the way most English speakers use the lens.