These days, a slightly better approach is to use the stringi package which provides a function for general unicode conversion. This allows you to preserve the original text as much as possible:
x <- c("Ekstr\u00f8m", "J\u00f6reskog", "bi\u00dfchen Z\u00fcrcher")
x
#> [1] "Ekstrøm" "Jöreskog" "bißchen Zürcher"
stringi::stri_trans_general(x, "latin-ascii")
#> [1] "Ekstrom" "Joreskog" "bisschen Zurcher"