This was a popular name in the 20th century (especially the middle decades) in French, German, and English-speaking countries. In the United States Christina has been more common since 1973, though both forms are currently floundering on the charts.
This is not the usual spelling in any of the Scandinavian languages (in Sweden and Denmark it is Freja and in Norway it is Frøja) but it is the common spelling of the goddess's name in English. In the 2000s it became popular in Britain.
As an English name, it became popular due to the Fleetwood Mac song Rhiannon (1976), especially in the United Kingdom and Australia.
In England, Sarah came into use after the Protestant Reformation. It was consistently popular in the 20th century throughout the English-speaking world, reaching the top of the charts for England and Wales in the 1970s and 80s.
Notable bearers include Sarah Churchill (1660-1744), an influential British duchess and a close friend of Queen Anne, and the French actress Sarah Bernhardt (1844-1923).