I plan on using formal and informal, though I am planning on doing it in all English. I know some use multiple languages, like English for casual and German for Schutzhund or French for French Ring.
You just need to be consistent and clear with the rules and expectations for each command. Also, as others have stated, dogs are masters at reading body language, tone and situational context so the command is paired with environmental factors. I do think it is possible to have a single command, however, you have to ask yourself, are you really asking the same thing of the dog every time? If you are actually asking for two different things (laying down near you at home on the couch vs a hard fast down in competition), I'd just put it to two different commands. Others have great success using only the one.
For example, COME will be my word for a casual come to me, like in my house, where as HERE is for a hard recall/performance recall where I want my dog to come to me and front. HEEL means we are competition heeling, if we go on a walk, we will practice general loose leash walking and then LEFT or RIGHT if I want my dog to do a casual heel at other side of me (depending on crowds/location I want to be flexible where I can put my dog in relation to my body). You can train a dog to do virtually anything if you make the rules really crisp and consistent.
The problem people sometimes have if you use, for example, HERE for both your at home and competition command is, unless you want and enforce your dog to constantly do a competition HERE, even when causally at home, on the field it might become confused and not perform as crisply, leisurely coming to you instead of doing a nice straight front.
Really it is all preference. What works best for you and your dog? If you feel like having multiple commands is too confusing for you, it will probably confuse your dog! Environmental cues should be enough that your dog can pick up on your intent, if you are consistent with the body language aspect of training.