That sounds great! As an icon I would suggest Я-A (which are both the last and first characters of the Cyrillic alphabet and suggests the transliteration from Cyrillic into Latin characters).
How should the transliteration table be formatted? I could make a table in Excel or Numbers with the mapping. Or is a .txt file better? Do you need additional information such as the HTML-code: č or Unicode HEX: U+010D for the č? And what to do with the capitals? Three Cyrillic characters have a transliteration into two Latin characters: Щ/щ → Šč/šč, Я/я → JA/Ja and Ю/ю → JU/Ju. This creates another problem: if for example the Щ is used in a fully capitalised word then the transliteration will be ŠČ. If, however, it is only the first character of a word that is a capital the transliteration would be Šč. For example the name Щедрин will be Ščedrin or, when capitalised, ЩЕДРИН, ŠČEDRIN. Hope this is clear.