Basically, any password is a string of letters and entropy can be easily calculated. For example you can use Shannon entropy calculator or by hand using scientific calculator.
Entropy is calculated based on frequencies of letters in the password, it do not care about used language. So diverse passwords with many different letters are preferred as entropy will be larger. Words are treated equally if they have the same proportions of used letters, e.g. English 'and' and Indonesian 'dan' has the same entropy). This means, contrary to what Poablo said earlier, that 'cryp5to' and 'crypto5' has the same entropy, entropy do not care about letter order. If you do not believe try yourself using similar examples into http://www.shannonentropy.netmark.pl
Of course, if attacker will assume that your password is word, not random string (most people do that) he will use dictionary to break your password and he will break it earlier, but his knowledge that you use word, not the random string is actually information which decreases entropy, he used external information to lower the entropy needed to brake it.
"Does the entropy of that part depend on the number of English words in existence, ..."
NO, it depends on the all combinations which can be done based on password length and diversity.
"... the number of English words known by the choosing algorithm..."
it may affect algorithm, but not from entropy point of view, e.g. if this algorithm will be: just try all words from dictionary in which there is no crypto5, but crypto is present, it fails, but if the algorithm is more cleaver, for instance take all words from dictionary and mutate them by random letter or number it will finally find crypto5.
" ... the number of English words assumed by the attacker?"
it may affect algorithm, but not from entropy point of view, see above, and remember you do not know who and how will hack your password, so you cannot assume anything like I will use different language, because it has more words, but on the other hand you can use different language if it has more letters (and you will use them in the password)
"Does the language matter, is the average entropy per word in German, French, Italian, or Spanish significantly different from the average entropy in English?"
You can calculate entropy for different languages (actually this is what Shannon did), but again it does not influence the entropy of the password.
"Does a numeric digit always have an entropy of log base 2 of 10 = 3.321928?"
No, base 2 is the most common, and it has nothing to numeric digits, it can be used also to letters or any other signs, see Wikipedia [information theory entropy]