Considering that no one can agree on how many genders there are, I think the only "solution" would be to have options of choosing "he", "she" or "they" as form of adressing yourself. It would involve some work in rewriting all texts, but it would be safe from new gender emerging tomorrow. And even that is only for English language. I don't know how French, German or Japanese languages are structured, but in my language (Slovenian) it would not be possible, as sex is reflected in many predicates, verbs and other parts of a sentence. And that sex only has three forms.