As for "energy" or "ki", I do defend the "spirit" translation as reasonably correct; the English term "spirit" matches reasonably closely in terms of usage. Like, it can be ethereal or purely psychological, for instance. It can refer to "energy" ("Do it with spirit!") or to "attitude" ("in good spirits").
My problem with "spirit" is that "ki" has spiritual, mental, and physical (tangible) meanings and all three are important in aikido. Spirit hits 2/3 at best, completely missing out the physical part.