x <- readLines(textConnection("ÁÀDFDS (artist 1)
1 Lorem ipsum dolor sit amet, consectetur adipiscing elit.
AB (artist 2)
2 Nulla sollicitudin elit in purus egestas, in placerat velit iaculis.
BBDDED (artist 3)
az*ù*ù*ù (bad string)
3 Nunc et eros eget turpis sollicitudin mollis id et mi.
4 Mauris condimentum velit eu consequat feugiat.
5 Suspendisse sit amet metus vitae est eleifend tincidunt.
ÉÈDFSF (artist 4)
6 Sed cursus augue in tempus scelerisque.
...gdgdgdg (bad string)
7 in commodo enim in laoreet gravida."))

x[grepl("^\\pN+|\\p{Lu}[\\p{Lu}']", x, perl=TRUE)]

cat("\n\n", paste(rep('-', 50), collapse=""), "\n\n")

x[grepl("^\\d+|(?![×Þß÷þø])[A-ZÀ-ÿ][A-ZÀ-ÿ']", x, perl=TRUE)]