I think the CMS designers are probably right. The problem is that it is perfectly possible that certain pages are not valid in other languages - the entire site structure MAY be different between languages, and so the current location is not necessarily valid in a new language.
Of course, your particular site may well be identical across languages, but if this cannot be guaranteed, the homepage is a good place to return to. You could, of course, include coding on your page to return to the same page in the new language, but I guess you are trying to avoid this sort of coding.
From a user perspective, I cannot see a good reason for wanting a specific page in another language, rather than the entire site. In other words, I think that the vast majority of users will navigate in the same language that they speak, so they will change language firstly - or very early - and progress from there. Changing language anywhere other than the home page is extremely rare ( I have seen, years ago, so evidence of this ).
So I think you are right to express concern and think about it, but in practical terms, I don't think it is a problem that will arise for many users.