In speech, I always use formulae as the plural of formula, mainly because it's occasionally useful to be able to distinguish easily between formulas and formulas', but for the others I use the plurals of the general forms ——ums and ——uses rather than ——a and ——i.

English is a great language to communicate in because there are so few conjugations and declensions, and the word gender is not a problem because just about everything not specifically related to males and females can be treated as neuter. But the finer details are a b*****, and deducing how to pronounce words from how they are spelled is a nightmare. For example, the combination of letters "ough" can be pronounced eight different ways, depending on what the rest of the letters in the word are. There's no way to work it out – you just have to learn the words and their pronunciation.