I have a bike whose rear wheel has "quick-release 5 x 135mm". Will I be able to replace this rear hub with an in-gear hub that has "Length 135 mm, Axis diameter 10 mm" (this is the N380 hub)?
With a quick release system there are two potential width measurements: the inner width of the axel (which a skewer fits into) and the outer width of the hollow axle. The "quick-release 5 x 135mm" likely refers to the width of the quick release skewer diameter/width and the "Length 135 mm, Axis diameter 10 mm" is referring to outer diameter of the axel which fits into the frame.
For your hub swap, the outer diameter of the axel is matters as this is what fits into your frame. As rear quick release systems used a 10 mm rear axel, the hub should fit.
Finally, if your frame is a quick release frame, you likely have vertical dropouts. These are not always compatible with internally geared hubs. You should ensure your frame is compatible with your internally geared hub.
Short answer - probably.
The two key measurements here are hub spacing and dropout size. This hub has the correct flange-spacing for your frame, but if your drop-outs cannot accommodate a 10mm axle you may still be able to use an adapter that takes the 10mm down to 5mm quick release at either end. This is a fairly easy to find after-market part but will not be as strong as a solid 10mm axle. Unless you are a really big guy or ride hard off-road I wouldn't be too concerned though.
The bigger concern is dropout style. Does your bike have horizontal or vertical drop-outs? You'll need some way to tension the chain, either with a single-speed specific frame (you can slide the wheel forward/backward to tension the chain) or a chain tensioner device (essentially the swing-arm portion of a rear derailleur).
So I'd suggest you first verify your frame supports a single-speed setup, then find the correct axle adapter. NOTE: most 9mm quick release drop-outs can fit a 10mm solid axle.