Translate any quotes that you think your audience will not understand. Give both the source of the translation and the original. Put the translation immediately following the quotation.
At the opening of Dante's Inferno, the poet finds himself in "una selva oscura" ("a dark wood"; Ciardi 28).
For content that you translate, add my trans. instead of a source in the parenthetical citation.
Sevigne responds to praise of her much admired letters by acknowledging that "there is nothing stiff about them" ("pour figees, ells ne le sont pas"; my trans.; 489).
If your paper includes a lot of content that you have translated, you might want to use an endnote describing which translations are yours. Put the endnote immediately after your first translation in which case you do not need to use my trans.
[information and sample quotes taken from Modern Language Association of America. MLA Handbook. The Modern Language Association of America, 2016, p. 90-91.]