Exophony
Exophony is the practice of (normally creative) writing in a language that is not one's mother tongue.
Some exophonic authors may be bilingual or multilingual from their childhood years, even polyglots, while others may write in an acquired language. In some cases the second language is acquired early in life, for example through immigration, and it is not always clear whether the writer should strictly be classed a non-native speaker. It is one form of transnational literature, although the latter also encompasses writing that crosses national stylistic or cultural boundaries without being written in another language.
It also overlaps with translingualism, and translingualist writer is one of many terms that has been coined to describe the phenomenon.
Some exophonic authors are also translators, including (in some cases) of their own works.