Hello,
Most of the love hotels are easy to use, even for non Japanese speakers.
You find one, get in, pick the room on a board with pictures (or on a screen). Then on to the room itself following flashing signs all the way (or to the receptionist that could only ask you potentially if you have a fidelity/member card).
When it comes to pay, cash is king. Some accept credit cards (even international ones) but most of people wants to avoid doing that for an obvious reason
For a lot of them, you have to pay in the room on a machine (pressing the "会計" button). Sometimes you pay at the reception but you'll only see the hand of the receptionist.
Very rarely will. you be in contact with an actual person (except some janitor staff walking around or other couples).
In Tokyo, I've used some on the back of Shibuya before (Dogenzaka) and they were easy to use. Osaka goes the same way, I would head for the area north of Kintetsu-Nipponbashi (right across the freeway), that offers tons of options a different price range.
Have fun!
