Football clubs playing in the league of another country
There are a number of sports clubs around the world that are based in one country/territory but play in another's league in their respective sport. Conditions for competing in a "foreign" league, as well as in a continental/confederational competition, are set case-by-case by the international sports federation as well as the respective confederation and national sport associations involved.
Clubs which are located in defunct nations that merged with others, new nations separated from others, or which stopped competing in a nation's league system because their locale was transferred to another nation, are not included in this article.
As a result of the history of football in the United Kingdom, the United Kingdom has four FIFA member countries instead of one. Therefore, clubs that play outside what would be regarded as their 'home country' are included.
...
Wikipedia