The English names for several languages include a RLM mark as they just replicate the native name (which is also incorrect in the first three cases), or just render the native name (autonym):
* [es-formal] = "español (formal)‎" (no RLM needed even in native Spanish!) – must be: "Spanish (formal)" in English
* [hu-formal] = "magyar (formal)‎" (no RLM needed even in native Hungarian!) – must be: "Hungarian (formal)" in English
* [nl-informal] = "Nederlands (informeel)‎" (no RLM needed even in native Dutch!) – must be: "Dutch (informal)" in English
* [sty] = "себертатар" – must be "Northern Tatar" in English
* [vo] = "Volapük" – should //probably// be "Volapuk" in English (without the combining diaeresis)
* [vro] = [fiu-vro]= "Võro" – should //probably// be "Voro" in English (without the combining tilde)
The following test page also HTML-encode the spaces to makes sure they are not duplicated in the middle (but this is not dramatic and not signaled as an error)
https://commons.wikimedia.org/wiki/Module_talk:Multilingual_description/sort/testcases
As a general rule, the English names of all languages should be plain ASCII only (of course, this does not apply to other translations or native names)...
This is also checked on the same test page where you can see the red cells in the last column) using the following basic regular expression:
/^[A-Z][ '()%-/0-9A-Za-z]*['()%-/0-9A-Za-z]$/
The reason for that is that the English names of languages is used in contexts where only ASCII is expected (spaces, parentheses, hyphens, single quotes, and slashes are still possible; applications are generally aware if these ASCII punctuations or spaces have to be replaced; decimal digits may occur in the name of some variants, like a year for an orthographic reform, but they generally don't cause problems)
Yellow cells on the test page jsut signal cases where the autonym and the English name are identical (not necessarily an error, but it may indicate a missing translation, either in English or in the native name; some of these cases are OK like "Esperanto", whose autonym is correctly capitalized for that language).