When you’re not feeling well or even if you just need a check-up, there is nothing worse than not feeling understood. Struggling through a consultation in broken German can add a huge amount of stress to an already difficult situation. Here in the greater Frankfurt area, we are very fortunate to have a lot of highly qualified doctors who speak another language in addition to German. And there is an easy way to search for a specialist who speaks your language of choice in the online database provided by Kassenärztliche Vereinigung Hessen. If you go to https://arztsuchehessen.de/ you can select the type of medical practitioner you need (under Fachrichtung), enter a postcode (Postleitzahl) and a radius (Umkreis) and then, under weitere Suchkriterien you can select language spoken (Fremdsprachen). You can also limit the search to a specific gender (Geschlecht), or search for places that are accessible. This database does not list doctors who only carry out private work. (This database does, but you can’t search by language: https://portal.laekh.de/arztsuche). But those listed in the arztsuchehessen database usually treat patients who are gesetzlich versichert and those who are privat versichert. Just remember that receptionists often don’t have the same language skills as the doctors, so try and at least start the phone call/conversation in German to “get them on side” while you stumble through the admin in your broken German/their broken English! If the practice uses the DoctoLib app, this can at least make the appointment-making process easier.
While the search tool for dentists doesn’t offer a language option, sometimes you can at least hazard a guess based on their name…! 
https://www.lzkh.de/patienten/zahnarztsuche
You will find a number of websites online that offer reviews of doctors and dentists (search e.g. for Bewertung Arzt). Personally, I would treat these with extreme caution, as you never know (1) whether the reviews are genuine, (2) what sort of people have written them, and (3) whether the nature of the reviews is representative or whether the few unhappy patients who made the effort to vent their upset online are far outnumbered by very happy patients who saw no need to spend time reviewing their doctor (or vice versa). You are allowed to change doctors if you are not happy with the one you first tried (with a few exceptions or limitations in certain cases, e.g. during pregnancy you can generally only change at the start of a new calendar quarter because of the way the health insurance companies pay the doctors). So don’t worry about being stuck with someone you didn’t feel happy/comfortable with.