This has been a mystery to me for some time. When should the Esperanto name of an island group receive the plural ending -J?

 - **Sejŝeloj, Filipinoj, Ferooj, Ŝetlandoj, Orkadoj, Falklandoj** are usually plural
 - **Fiĝio** is [sometimes][1] in the singular, [sometimes][2] in the plural, **Fiĝioj**
 - Lots of island groups are always in the singular: **Mikronezio, Tuvalo, Malto** (cf. the English expression *the Maltese Islands*)

I guess that some of these names are shortened from the expression ”-***aj insuloj***”, like **Feroaj Insuloj** > **Ferooj**. But the same expression could be used with any of the above names, e.g. **Mikroneziaj Insuloj**. And while we’re at it, why not **Japanioj** for Japan, another island group? The whole system seems very chaotic to me; hope somebody can help. :-)

  [1]: http://www.simplavortaro.org/vorto/Fi%C4%9Dio
  [2]: https://eo.wikipedia.org/wiki/Fi%C4%9Dioj