I think the comparison to a foreign language is apt. And after studying in classes (never visiting a fracophone country), I was able to translate for someone who visited the hotel I worked at in college. Was I great at it? No. But then I'd only had a few years of experience and not a lot of practice.
I don't think there's any way to say that "a diverse array of real world experience" is necessary nor to measure its helpfulness, since most people will never have a chance to gain such a diverse array in the real world - at most, they can expect to use their physical skills once or twice unless they are a bouncer, LEO, or other profession that puts them in those situations on a regular basis. Does real world experience help? Yes, that seems almost certain, but it's impossible to tell how much. It might be a lot. It might be a little. There are too many other factors at play to make a valid conclusion on that, since we can find plenty of examples of martial artists from TMAs and similar training who competently handled themselves in real world situations without having any past experience in real world situations of physical defense.
When I say a "diverse array of real world experience" in the context of training Martial Arts, I should probably better define this, because, of course, I'm not expecting practitioners to go out and get in street fights or some nonsense, nor do I think such experience should be limited to LEO and bouncers. What I mean is practicing in a RBSD sort of setting/environment, or even just varying your training with your friends and experimenting; learning to deal with things intuitively, and becoming familiar with using the concepts and instilled habits of your art freely.
The trap that I think many Aikidoka and even TMA artists in general fall into is just practicing rigid technique where A does X and B does Y. I'm speaking of training where A does, and continues to do whatever he/she can to challenge B, and B learns to adapt and flow. But this should not take the form of mutual sparring, if you are attempting to practice skills that may be useful for self-protection (and a sparring format is not really suited to Aikido in the first place) -- rather, A should consciously take the role of the attacker and focus on developing his/her training partner. It's useful to do this with people who have not trained your particular art, because often trained habits of an uke are very different from that of your average person, or even martial artist, and you may find that you have difficulty making many of your locks/controls/throws/etc. work, and need to adapt.
I'm surprised that you had such success with translating French, though! I've mostly studied languages that are not in any way related to English, so I suppose it's more difficult to adapt with them. Granted, you can get by with really basic fluency if you're very creative and are just using communication as a basic means to an end. As for actually being able to use a language naturally and being able to engage in a diverse array of settings and activities that you might meet in every day life with fluency, I still stand by my assertion that you have to experience and familiarize yourself with those things, and I think our goal in martial arts should be somewhat similar.
I think that most people over specialize and refine their practice, whereas our true aim should be to diversify it and make it naturally intuitive and adaptive to any situation (as opposed to one, very specific situation/context). Martial Arts should impart general concepts, mindset, skill, and ability, rather than specific recipes.
One more quick analogy; cooking.
Most people are quite fond of cooking with recipes, and I think that is a sort of low-level, unreliable, and unskilled method of cooking. Recipes are aids for beginners or people who haven't made a particular dish before, but we should aim to be able to cook intuitively, and adapt to the situation (what ingredients we may or may not have at hand).
I actually get quite frustrated with recipes, because it's sometimes difficult to separate the essence of a recipe from the fluff. Recipes given to you might often be very complex and specific, with lots of ingredients and specified amounts. But what ingredients are non-essential additions? What other ingredients might the recipe benefit from? What ingredients are essential for the essence of the dish? What substitutes might work? How might the amounts vary, depending on the quantity that I am making or the varying strength or size of my ingredients? What do I do when I follow the recipe to the T and for some reason it just tastes bland, or the flavors are out of balance?
Formal training is like giving someone a handful of recipes. But how does one use them in real life, intuitively? By becoming familiar with cooking, and the ingredients as a whole, using the general concepts and guidelines found in those recipes. You learn what components are essential, what ingredients are related and how they interact or balance out one another; you get an intuitive feel for how much of this or that to add, and how to balance out flavors when something is amiss. And, you develop an intuition that can go beyond the scope of your current list of recipes, and can create entirely new things on the fly.
I'm to the point with cooking that, at most, I will glance over recipes for inspiration, if I consult them at all. I don't measure anything, and I can come up with something almost regardless what ingredients I have at hand. I regularly experiment and rely solely on intuition and experience, and rarely do even my boldest experiments go awry.
Martial Arts are no different -- at least, for me, and my goal is to develop them in the same way that I've developed my culinary skills. I want not just the curricula, but the essence of what that curricula is meant to impart.
