Sensitive multilingualism
It is phenomenon of understanding but not communicating in non-mother-tongue languages. It usually happens in countries or territories which enjoy high life standards and appear to be a paradise for millions of immigrants from other states. It nearly always takes place in current EU and USA that became an immigrant heaven a long time ago.
Provided a family with one or two children arrives from an unstable Asian or African country and stops at one of the above-mentioned regions, children have to acquire a new language immediately. What's more, he starts going to school where all the subjects are taught in a new language. No wonder that dwelling in a foreign language community makes him learn a new language very quickly and forget mother tongue (if not practiced within family). As a result, there appears a situation when person co-exists in double language atmosphere and there are two variants of ending-up of this problem. An offspring masters either one of the languages (depending on the corresponding language practice) or becomes an expert at both of them. But it's rather unusual even for this kind of situation to end up in complete losing competence in either of languages.
A standard situation is when a child becomes much better at the new language due to understandable conditions but doesn't forget mother tongue. In that case, we have the phenomenon of sensitive or receptive bilingualism (multilingualism) that is extremely widely-spread in politically- and economically-advanced countries.
Eventually, we see over-populated Paris and London, for example, which constantly face massive immigrant strikes that draw in scuffles, arrests, deportation and so on.
