I'm writing a package function where I want to check if some text contains any of the following characters:

äöüßâçèéêîôûąęćśłńóżźžšůěřáúëïùÄÖÜSSÂÇÈÉÊÎÔÛĄĘĆŚŁŃÓŻŹŽŠŮĚŘÁÚËÏÙ

Problem is that devtools::check() returns a warning:

W checking R files for non-ASCII characters ... Found the following file with non-ASCII characters: gb_data_prepare.R Portable packages must use only ASCII characters in their R code, except perhaps in comments. Use \uxxxx escapes for other characters.

So I tried to convert these characters into unicode, but actually don't really know how.

stringi::stri_encode("äöüßâçèéêîôûąęćśłńóżźžšůěřáúëïùÄÖÜSSÂÇÈÉÊÎÔÛĄĘĆŚŁŃÓŻŹŽŠŮĚŘÁÚËÏÙ", to = "Unicode")

Error in stringi::stri_encode(x, to = "Unicode") : 
  embedded nul in string: '\\xff\\xfe\\xe4'

doesn't work. Same with

iconv("äöüßâçèéêîôûąęćśłńóżźžšůěřáúëïùÄÖÜSSÂÇÈÉÊÎÔÛĄĘĆŚŁŃÓŻŹŽŠŮĚŘÁÚËÏÙ", from = "UTF-8", to = "Unicode")

Error in iconv(x, from = "UTF-8", to = "Unicode") : 
  unsupported conversion from 'UTF-8' to 'Unicode' in codepage 1252

Any ideas what I can do?

Note: weird thing also is that if I do:

x <- "äöüßâçèéêîôûąęćśłńóżźžšůěřáúëïùÄÖÜSSÂÇÈÉÊÎÔÛĄĘĆŚŁŃÓŻŹŽŠŮĚŘÁÚËÏÙ"

x now returns "äöüßâçèéêîôûaecslnózzžšueráúëïùÄÖÜSSÂÇÈÉÊÎÔÛAECSLNÓZZŽŠUERÁÚËÏÙ" which is wrong. So I guess it also has something to do with my general R encoding?