Many languages distinguish between inclusive and exclusive first-person plural pronouns (“we”). (Click or tap here to see more details)
The inclusive “we” specifically includes the addressee (“you and I and possibly others”), while the exclusive “we” specifically excludes the addressee (“he/she/they and I, but not you”). This grammatical distinction is called “clusivity.” While Semitic languages such as Hebrew or most Indo-European languages such as Greek or English do not make that distinction, translators of languages with that distinction have to make a choice every time they encounter “we” or a form thereof (in English: “we,” “our,” or “us”).
For this verse, translators either select the inclusive form (including Theophilus) (according to Velma Pickett and Florence Cowan in Notes on Translation January 1962, p. 1ff.) or the exclusive form (according to SIL International Translation Department (1999)).
M. John (in The Bible Translator 1976, p. 237ff. ) explains the difficulty of the choice this way: “Here the translator working in a language with the two forms of we has to make his choice, at least in part on the basis of the answer to the question whether Theophilus was, at the time of Luke’s writing, a Christian. The choice of the form of we and the translation of the last part of the paragraph (Luke 1:4) are interconnected.”