I've thought about this and tried to answer a few different times when it comes up. I'm a native english speaker and I can use a few other languages to various (mostly pathetic) extents. But I also have a well-developed spatial sense, to the point where I basically never get lost because I can just about always simply visualize where I am in my memory of surroundings that been assembled in my headspace, and those "which of this figures is figure A viewed from a different angle" questions on mental acuity test is on the level of "why is something this obvious even a question". Also I have pretty well-integrated synesthesia that seems to significantly contribute to perception of letters, colors, textures, words, shapes... But I've found that it does not seem to contribute at all to syllabary or concept-glyphs which makes understanding japanese, chinese, and cherokee difficult. Any way, the point of that is to get at saying that I do not have an inner monologue that plays out in my head in my native language most of the time. Sometimes when mentally drafting a text or thinking in clearly defined steps. But for the most part it's a sort of symbolic language that's a combination of flashes of the sensory impressions of words and concepts, shapes, links, and interactions. I definitely have an inner monologue, but not like I hear most people describe theirs. And I definitely do not lack an inner monologue, at least based on the descriptions I hear of others who lack one and are able to meaningfully contribute to discussion on it.