Because ionization is a word only used in scientific speech, there is no answer for this that fits common situations. As user The Photon suggests, for scientific terms you will just have to customize it for your region, and sometimes even your particular professor.
Physics has a number of words that fall under this rule (for example, "fusion" can refer to either nuclear combining of atoms or the melting of a solid, depending on the age of your textbook), which is difficult given the need for precision in the science.
I do not know of a dictionary that covers spelling differences between the languages, but I suspect that a search of this particular Stack Exchange would cover the majority of them that exist.