the whole mother machine line is a poorly written joke, someone might even think that BW can't write a game without involving ancient civilazation that is somehow involved in creation/destruction of modern species. Nowhere in SW lore is something like this mentionend, but then again, SI storyline is full of inconsistencies

and all this proves how little BW knows of actual SW lore. Look at the TotJ comics and you can clearly see that there are no humans in the empire - how humans became a dominant species in the empire is a mystery beyond this world. All of the original Sith Lords were human-sith hybrid, or how this game calls them - purebloods. Considering that your ancestor Kallig was a Sith Lord of the old empire it should be very likely that your SI character is 'pureblood'. Same goes for the SW

you have to remember, above else empire is meritocracy. So even if you're ancestors were non-humans or non-sith(species) it doesn't matter. What matters is if they proved to be strong enough force users.

there is no explanation, Star Wars universe is full of such weird examples. C-3PO is the one who did most of the translation in the movies - from R2-D2 to Jabba. We can only assume that ppl speak multiple languages, but considering how many species Star Wars has, it is a bit streched language system is not so deneloped in SW as it is in some other Sci-Fi or Fantasy franchises