What's a good regex to include accented characters in a simple way?

Accented Characters: DIY Character Range Subtraction

If your regex engine allows it (and many will), this will work:

(?i)^(?:(?![×Þß÷þø])[-'0-9a-zÀ-ÿ])+$

Please see the demo (you can add characters to test).

Explanation

(?i) sets case-insensitive mode
The ^ anchor asserts that we are at the beginning of the string
(?:(?![×Þß÷þø])[-'0-9a-zÀ-ÿ]) matches one character...
The lookahead (?![×Þß÷þø]) asserts that the char is not one of those in the brackets
[-'0-9a-zÀ-ÿ] allows dash, apostrophe, digits, letters, and chars in a wide accented range, from which we need to subtract
The + matches that one or more times
The $ anchor asserts that we are at the end of the string

Reference

Extended ASCII Table

A version without the exclusion rules:

^[-'a-zA-ZÀ-ÖØ-öø-ÿ]+$

Explanation

The ^ anchor asserts that we are at the beginning of the string
[...] allows dash, apostrophe, digits, letters, and chars in a wide accented range,
The + matches that one or more times
The $ anchor asserts that we are at the end of the string

Reference

You just put in your expression:

\p{L}\p{M}

This in Unicode will match:

any letter character (L) from any language
and marks (M)(i.e, a character that is to be combined with another: accent, etc.)

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