(written from a Production point of view)
Trent Pehrson is an American linguist who constructed the Romulan language as it is spoken and written Star Trek: Picard.   Pehrson also served as a dialect coach for the language, for which he received an on-screen credit in the series.
While previous Star Trek series and films had used small fragments of Romulan language and Pehrson used these (as well as preexisting fragments of Vulcan language) as a basis for his work, he constructed most of the Romulan grammar, phonetics and lexicon himself for Star Trek: Picard. 
Aside from his Star Trek work, Pehrson is known for creating his personal constructed language called Idrani.