Romance languages transliteration plugin

[Carlos]

I suppose the lang authors could simply add this to the lang file also ?

Yes, in fact there are several language files that do it.
But if an user has a different language selected for the backend (e.g. he or she prefers working in English), then transliteration doesn't work for this user.

since GS now has i18n fallbacks to default ( which is core en ) COuld be not just add this to the core en_us file, i think its missing.

Yes but... for all languages? Only some?
There's also a problem with at least one character: ü (and Ü) - in German it is transliterated as "ue", but in Spanish it should be "u". No idea if there are other possible conflicts between langs.