Is it purely an analysis tool? I assume one must load the data from a GPS receiver recording device?
You right. You just use your favorite GPS and then can see many details on phone or tablet. I try to cover many file formats to get convient tool

Or can it accept data from a GPS vis Bluetooth connection in real time?
no. Only pre-recorded track needed. It is for windsurfing basicly, you can't use many devices while riding.

Does it calculate and display the standard GPS-SS and/or GPS-TC categories? (max speed, 2 sec, 10sec, 5x10sec, 100m, 250m, 500m, Nautical Mile, Alpha500m, 1hr, total distance )
Yes, It calculates speed on different distances. Look 3d picture. There is scroll with speed analysys. You can croll it down to see up to 500m. No Alpha yet.
Total distance are on first page with other global info

How do you import the GPS data into the device the app runs on?
There are many ways, depend on wich GPS logger you are using. If you records on same phone with loggers so you do not need nothing at all.
Im use it by 2 ways - records track on cheap android, upload track to GoogleDrive, and on big screen phone open this track from google drive.
For Garmin watch - im use Ant wireless interface (similar to bluetooth) to download track to phone and GoogleDrive (at same time). So later I can open this track on any phone or even from desktop.
If you device can be as USB masstorage (work as usb flash) - you can download track directly by the cable
For GT-31 you can use USB cardrider, connected directly to phone, or download files on desktop to cloud drive and then open tracks from android phone/tablet
You can open attach from emails, track can be transfered from other android app via sharing feature.
You can see more details here - www.facebook.com/Windsurfing.Track.Analyzer/

Is there and English language version?
Of cause it have. But may be with some my errors )

What are the main differences between this app and GPS-Logit?
Mine is not record track at all. Supports many gps types. I plan to adapt it to 5/10hz files. I try to cover as many ways to open files.
GPS-logit can't do this, and android gps logger are not too good for speed sports, because of lagging.
Mine have sharing feature, so you can share yours resutls with your friend in facebook, insta, email, viber, whaterver.
Mine looks better )))

I can send you some 5Hz GW-52 (.sbp) files. Also some uBlox UBX files in various Hz rates from 5Hz to 18Hz if you need them for development.