This issue can be avoided by following the ISO standards ISO-31 and ISO-80000-1. Under these grouping is done by separating groups by a small space (U+2009, THIN SPACE, is usually used, I believe). If there is a period or comma in the number, it is then unambiguously the decimal separator.
We should even already be used to that style, because those are the standards that cover how SI units are supposed to be written.
So just write it as 10 000% and everyone should be happy.
You'll love Apple's smart new "Touch Space Bar", which lets you continuously adjust the width, style and semantics of Unicode spaces from zero width, hair thin, various EM&ENs, to obesely fat, pregnant pause, breaking, non-breaking, numeric, oghamic, figure, ideographic, word, punctuation, visible, ␠ symbols, mathematical, poetic, scientific, pseudo-scientific, streaming, auto-repeat, lossless and lossy compression, deep, personal, safe, digital rights management, Mongolian vowel separators [1], etc, simply by swiping, tapping, crossing and snapping your fingers, while watching the mesmerizing colorful blinking graphical feedback provided by applications supporting the NSTouchSpaceBar API.
Microsoft also has a dog in the space race: see their "Space Characters Design Standards". [2]
OK, some do in this table, but I'm not sure how accurate it is.
It lists my country as one of those countries, and we definitely don't use space as thousands separator (we use period).
Perhaps what the table shows is just that this is the "SI style", and assumes that countries whose scientists and units follow the SI also follow this way of thousands separators, but we don't. We just use the SI units -- and even our scientists use period for the separator.
We should even already be used to that style, because those are the standards that cover how SI units are supposed to be written.
So just write it as 10 000% and everyone should be happy.