It is an interesting exercise to write in a second language. Writers like Beckett, Conrad and Nabokov did it. Maybe for some writers the sense of estrangement helps. Maybe, beyond a conscious intent to “translate”, there’s also an unconscious transit between the two languages that results in something else, some sort of hybrid form, similar to grafting? I am thinking of the Latin term “translatio” meaning to carry over, to transfer, transport, to convey. In this sense, “translation” is always a plus. There’s always something to be gained, rather than lost.
If there is such a thing as an “authentic” language, I dare say it is the one that comes from one’s heart. And the heart of an immigrant is, to awkwardly appropriate the words of the English Bard, “an isle full of other noises, sounds, and sweet airs.”