There are few cities in Europe where minority languages are used as the main language. Instead they’re spoken mainly in rural areas where jobs can be hard to find, so it’s not uncommon for speakers of such languages to move to cities for work. Not all of them will continue speaking their languages and they may not return to their original homes, at least until they retire.
The strongest minority language in Europe is Catalan, which is the main language of a number of cities, including Barcelona. Other minority languages are not in such a strong position.
So you might say Teanga gan cathair, teanga gan todhchaí (A language without a city is a language without a future) – this is an up-dated version of Pádraig Pearse’s saying Tír gan teanga, tír gan anam (A country without a language is a country without a soul), which I found today on a blog post discussing this topic.
In Ireland, for example, the main places where Irish is spoken by a significant proportion of people, the gaeltachtaí, are in rural areas where jobs tend to be few and far between. As a result, they’re suffering from depopulation. The only gaeltacht in an urban area is in Belfast and it’s apparently thriving.