How would I say "Sorry, I don't understand" in Japanese?
I know wakarimasen means I don't understand, but what's the equivalent of making it apologetic? Would it be something like wakarimasen gomennasai?
It depends on who you're talking to. I would opt for the word 'sumimasen' here if you're talking to someone older or someone you don't know too well, as in: "Sumimasen, wakarimasen (deshita)." (You can use the 'deshita' if you want to say "I didn't understand you," although you can just leave it out if you want to say "I don't understand you.")
Here's an article about sumimasen that you might find helpful.
"sorry, i don't understand." => "sumimasen, wakarimasen.".
"sorry" => "sumimasen".
"understand" => "wakarimasu".
To make it negative, convert "...masu" to "...masen".