If you want redirect two separate domains to the same subfolder using .htaccess, you can use the code below by changing domains and folders to match your situation.
<IfModule mod_rewrite.c>
RewriteEngine On
Options +FollowSymlinks
RewriteBase /
# Redirect PuistoSahlynSM.fi
RewriteCond %{HTTP_HOST} ^(www\.)?puistosahlynsm\.fi
RewriteCond %{REQUEST_URI} !puisto/
RewriteRule ^(.*)$ puisto/$1 [L]
# Redirect PuistoSählynSM.fi
RewriteCond %{HTTP_HOST} ^(www\.)?xn--puistoshlynsm-hfb\.fi
RewriteCond %{REQUEST_URI} !puisto/
RewriteRule ^(.*)$ puisto/$1 [L]
</IfModule>