B1
除了…以外 — except, and also
How 除了…以外 means both “apart from” and “besides” in Chinese, and why 都 or 還 in the second clause is what tells the two apart.
除了…以外 sets something aside. What is not obvious is that it can set it aside in two opposite senses — excluded from what follows, or added to it — and the pattern is identical. The adverb in the second half is what decides.
With 都 — everyone except
除了我以外，大家都去了。
Chúle wǒ yǐwài, dàjiā dōu qù le.
Everyone went except me.
除了星期天以外，我每天都上班。
Chúle xīngqītiān yǐwài, wǒ měitiān dōu shàngbān.
I work every day except Sunday.
都 gathers up everything that is left once A has been removed. The thing named is out.
With 還 or 也 — and that as well
除了中文以外，他還會說日文。
Chúle Zhōngwén yǐwài, tā hái huì shuō Rìwén.
Besides Chinese, he also speaks Japanese.
除了小雨以外，小明也來了。
Chúle Xiǎoyǔ yǐwài, Xiǎomíng yě lái le.
As well as Xiaoyu, Xiaoming came.
還 and 也 add to what was named rather than removing it. The thing named is in, and something else joins it.
除了我以外，大家去了。
除了我以外，大家都去了。
Without 都, 還 or 也 the sentence never says which of the two meanings it has. The adverb is not decoration here — it carries the whole difference between everyone except me and me and everyone else.
以外 is often dropped
除了 alone is extremely common in speech and means the same thing. 之外 also appears, and is a touch more formal.
除了他，我們都同意。
Chúle tā, wǒmen dōu tóngyì.
We all agree apart from him.
What cannot be dropped is the second half’s adverb — which is the opposite of what an English speaker expects, since except me, everyone went needs no extra word at all.