The Greek that is often translated as “appoint” in English has the option of various terms in Luang with different shades of meaning.
For Mark 13:20, “naliri-natoha” (“choose-move”) was chosen. This is used if “choosing something to set aside for future use, with the additional idea that there are a large number of objects being chosen as opposed to only one and connoting separating/sifting of the good from the bad.”
For Acts 4:12, “ntutmata-nkewra’a” (“point eyes-lift chin”) was chosen. This is used when “appointing one special person to do a very special job that no one else can do. The focus is also on a special person doing the choosing. This is often the term used in verses that speak of what Jesus Christ was appointed to do and of how Paul was an apostle chosen by God.”
For Acts 14:23 and Titus 1:5, Rana (“lift up”) was chosen. This is used for “people choosing people to be over them. This is often the term used for the appointing of elders of the church.”
Source: Kathy Taber in Notes on Translation 1/1999, p. 9-16.