I have problems analyzing the constituents of the following sentence: 德国人不习惯他们旁边围满了人 I cannot understand in this sentence the various functions of the components. 

德国人不习惯他们旁边围满了人

I understood the meaning ("Germans are not used to be surrounded by a lot of people", non-literally) but I can't well understand the structure. 

Up to 他们旁边 it's fine: "their side". Now there's 围, and I can't understand if it's here as a verb or as another noun. In this last case, it would be determined by 他们旁边, and we could maybe translate it as "their immediate surroundings", since 旁边 gives me the idea of "very close". At this point though, 满 must be the verb, but Pleco says that, as a verb, you can use it only to express the meaning of "to fill" (unlike 充满， that actually would work better since it expresses "be filled with"). But if this is the case, its object should be the object that it fills, like a cup. 人 has no sense as an object in this case.

Maybe 满 is a complement for 围? Can be used as a complement? And why the use of 了?
德国人不习惯他们旁边围满了人。
Germans are not used to having a lot of people around them.

(whoever wrote this has never been to the Oktoberfest or any Bierfest)

A Chinese sentence does not have to conform to the grammatical standards of English.

德国人
Germans
不习惯
not used to
他们旁边围
their surroundings
满了人。
full people