What is the meaning of -ien?

Noun pluralization suffix; sometimes with vocalic ablaut in the pluralized noun

forms nouns denoting where something or someone is from; -ian

forms adjectives indicating relation to; -ian

Used to form country names; -ia

Used to form the plurals of some neuter nouns of Latin descent whose original plural ends in -ia.

Forms nouns and adjectives denoting origin, association, or residence; -ian.

Source: wiktionary.org

See also