I've seen some escort ads in newspapers written in other languages, but other than that, how do non-TER agencies advertise and get business?

The majority of escorts advertise on escort mall sites and erotic magazines or papers. The ads work for them, most men that seek escorts do not use or know escort review sites.

Print ads in "trade papers", lots of client referrals, trading clients, talking/giving "cuts" for new clients. This profession has been around a loooong time. The Internet is just the newest and best mouse-trap to date.