Why would the figurative language used in Mary Shelley's Frankenstein be fitting for the Romantic (Romanticism) period?
The figurative language found in Mary Shelley's Frankenstein was fitting for the period based upon the different characteristics illustrated by authors on the period. Romantics adored the imagination, individualism, and the power of nature. Given that some of the themes prominent in Romanticism were the inclusion of dreams and visions and Pantheism, Shelley's use of figurative language was of the utmost necessity.
Through the use of Victor's imagery filled dreams, readers are able to see what is to come through the use of foreshadowing. Not only that, Victor's numerous illnesses were only cured through the beauty of nature: "he [Clerval] again taught me to love the aspect of nature" (often illuminated by Shelley's immaculate descriptions of the natural world surrounding Victor.):
When happy, inanimate nature had the power of bestowing on me the most delightful sensations. A serene sky and verdant fields filled me with ecstasy. The present season was indeed divine; the flowers of spring bloomed in the hedges, while those of summer were already in bud. Chapter 6
Shelley's setting depicted those which "were among the favorite landscapes for Romantic writers" (Enotes Style Guide on Frankenstein).