Also remember that \p{Lu} and \p{Ll} can be used to match any uppercase (and consequently, lowercase) letter in any language without requiring the *UCP switch (in Sigil's PCRE regex engine).
\p{L} matches any letter (Unicode or otherwise) and \P{L} matches anything NOT a letter.
So (\p{Lu}{2,}) should theoretically do the same thing (not near a machine to verify syntax).
See the Unicode Categories section of
https://www.regular-expressions.info/unicode.html for more categories.