Add this rule as the first rule in your DOCUMENT_ROOT/.htaccess:
RewriteRule ^nl(/.*|)$ http://www.domain2.nl/? [L,R=301,NC]
Another tip about regex:
You should change your regex to use: [\w-]
instead of [A-Za-z0-9-_]
since:
- Hyphen should be first or last characcter in character class to avoid escaping
\w
is equivalent of[a-zA-Z0-9_]