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