Esperanto
There are two remedies of this problem, both of which use digraphs for the letters with diacritics. Zamenhof, the inventor of Esperanto, devised an "h-system", which replaces ĉ, ĝ, ĥ, ĵ, ŝ, and ŭ with ch, gh, hh, jh, sh, and u, respectively. A more recent "x-system" has also been used, which replaces ĉ, ĝ, ĥ, ĵ, ŝ, and ŭ with cx, gx, hx, jx, sx, and ux, respectively.