SACC policy on diacritical marks on English names
Because correct pronunciation of English names with respect to accents on syllables is not guided by accent marks, we do not use accent marks on many words, mainly place names, that require them in Spanish or Portuguese (e.g., Apurimac, Baudo, Choco, Junin, Merida, Paramo, Rondonia, Tachira, Tucuman). Part of the rationale for their absence is that pronunciation of English names that incorporate unfamiliar Spanish or Portuguese words that do not have accent marks (e.g., Tacarcuna, Jabiru) still requires knowledge of the rules of those languages to accent the proper syllable.
Other names that require diacritical marks in Spanish are also considered proper English words, without accents (e.g., Galapagos), as in the Oxford English Dictionary; in fact, placing an accent on these words in English would technically be a misspelling.
We do not use a cedilla in "jacana" or "aracari" because the Oxford English Dictionary treats these as English words without a cedilla.
(1) We use tildes on "Marañon" and "Nariño" because neither are English words, and correct pronunciation of the letter sounds requires them.
(2) We retain the tilde on "São Paulo," because English dictionaries typically retain the tilde even though not really necessary for pronunciation. For consistency, we also retain the tilde in São Francisco Sparrow."