Isla is a hit name throughout the English-speaking world but hasn't found the same popularity in other western countries, perhaps because its spelling and pronunciation don't make sense for those whose native language is not English. Think island without the final two letters.

Sofia is a refined variation of the Greek name Sophia, which was derived directly from sophia, the Greek word for wisdom. It was the name of a Roman saint—the mother of Faith, Hope, and Charity—and queens of Russia and Spain.

Most of the notable Rivers have been male, but this nature name certainly flows as well for a girl. The name River is still rising for both genders, with about 3500 baby boys receiving the name last year vs. 1900 baby girls.

Arya was derived from an Indo-Iranian word meaning "Aryan" or "noble." It is a masculine given name in Iran, Indonesia, Bali, and Sanskrit-speaking regions of India. In Hindu- and English-speaking parts of the world, Arya is more often a feminine name, the latter influenced by the similar Italian name Aria, meaning "air" or "song."

Lilian is the far less popular than the 'Lillian' spelling. To avoid a lifetime of mistakes and misspellings, we suggest you go with the Lillian spelling, which also looks more polished on paper. Whichever spelling you prefer, these names are benefitting from the fashion for girls' names starting with L.