Synonyms of 'fluency'
1 ability to speak or write, good command, articulatenessTo work as a translator, you need fluency in at least one language.
ability to speak or write
2 easeDictionary, control, facilityHe was praised for speeches of remarkable fluency.
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Your command of something, such as a foreign language, is your knowledge of it and your ability to use this knowledge.
His command of English was excellent.
Thesaurus for fluency from the Collins English Thesaurus
the quality of being fluent , esp facility in speech or writing