This isn't necessarily a fixed translation, per se, because the word just means a key that is "remote" from the current one, and could possibly be "written around" a lot more effectively.

The more distant a key is, the more notes it might have in common with the original key (hence the 機微 - subtleness), which makes changing keys, or "modulating," easier (or at least more pleasing to the ear).

"The modulation to a distant key in the statement of the <italics>moderato<italics> theme, which picks up the/a drawn-out melody, is beautiful in its subtlety and recalls the/a motif from the cadenza part of the way through." (Sorry for the literalness, but I need more context.)

Note: I'm guessing "modere" is "modéré," which would indicate a French composer. In English, we generally stick to the "accepted" (i.e., Italian) designations ("allegro" etc.), as opposed to whatever the composer decided to stick in his work (unless it's Erik Satie, who used some very "outside-the-box" indications for tempi and mood), which is why it might be better to change the "modéré" to "moderato," although you'll have to make that decision based on whatever other information you have available.