Language as such has nothing to do with the CW speed measurement STANDARDs. In amateur radio we are oblicated to use plain text (encryption is not allowed), so the standard word PARIS is used to check CW speed and CODEX word does not apply. OK, the PARIS word may (or may not) have been originally based on English language, but you do not need to concern yourself about that. If you have a WPM count, multiply it with 5 to get CPM and if you have CPM count, divide it with 5 to get WPM.
In real life many (if not most) plain text langugaes do not produce the correct CW speed, if calculated (or measured) from a length of text. That doesn't have any significance, however. The PARIS (and CODEX) words are the STANDARD, to which all CW speed measurement is based, so do not try to use anything else for CW speed testing, or you will get wrong results.
By the way, what we now call (International) Morse code, was NOT created by Samuel Morse. His wire telegraph code had significant differences to the CW code we use today. The international telegraph code, to which our over-the-air CW is based today, was agreed upon at a conference in Berlin in 1851.