"sorry, i don't understand." => "sumimasen, wakarimasen.".
"sorry" => "sumimasen".
"understand" => "wakarimasu".
To make it negative, convert "...masu" to "...masen".
"sorry, i don't understand." => "sumimasen, wakarimasen.".
"sorry" => "sumimasen".
"understand" => "wakarimasu".
To make it negative, convert "...masu" to "...masen".