In reply to tonanf:
English words should have English plurals. "Crux" is an English word (from a Latin origin). So it should have the English plural "cruxes", not the Latin plural "cruces".
Interestingly (well, perhaps), the climbing use of the term crux is historically a borrowing from a textual critics' use. A textual crux is a key bit where the manuscript is unclear, a vital point in supporting an interpretation. And the plural in that context IS "cruces".
A Level pedantry tip: if you ever catch anyone trying to pluralise "status" or "impetus" as "stati" or "impeti", you can have a good laugh at them, because the Latin plural of "status" is "status" (with a long U).