This word has two opposite meanings depending on its partner. besides除了 X (apart from以外) sets X aside; then the adverb in the second clause determines what happens to it. With all / both都, X is excluded ("everyone except X"); with still / also还 / also也, X is included and added to ("besides X, also …"). The apart from以外 is optional.
Structure: 除了 + X (+ 以外) ,Subject + 都 / 也 / 还 …
except for除了him他we,我们all都have been去过。
Except for him, we've all been there.
besides除了Chinese中文he,他also还can会speak说Japanese日语。
Besides Chinese, he also speaks Japanese.
remember: the second word flips the meaning. besides除了…all / both都 = "except" (X is excluded); besides除了…still / also还 / also也 = "besides" (X stays, plus more). Read the all / both都 / still / also还 before deciding which sense of "besides除了" applies.
Watch out
- apart from以外 (or outside之外) is optional and changes nothing.