In 7th Sea 2e, the books seems to indicate that sorcery is tied to where you are from. This seems to implied you have the sorcery of your region and only that of your region. However I found nothing explicitly stating that. Is there anything to indicate that either RaI or RaW, characters can have only one type of sorcery or are they allowed as many as they can buy advantages for?
By RAW, you can only have sorcery from a single nation.
In character creation you choose a nation for your hero (as part of step 0).
This choice impacts the trait bonus that you receive during step 2, as well as impacting the costs of several advantages.
The wording clearly intends for each character to have a single nation, and there does not appear to be any provision for multinational characters.
Meanwhile, the Sorcery advantage gives you "the Sorcery from your National bloodline."
Contrast this with Duelist Academy, which begins with "you may choose a Dueling Style."
I'm unsure of RAI, and you're always free to rule otherwise. I don't know what the repercussions of allowing sorceries to mix would be, but it's probably something that could be made to work.
A character can only have one type of Sorcery.
Source: I wrote the Sorcery framework. Also, page 150 of 7th Sea: Second Edition states "You gain the Sorcery from your National bloodline." This only could "conflict" with the Foreign Born advantage (page 148) which allows a Character to have grown up in a different Nation. In that case, the character's National bloodline is still the one they selected in Step 2: Nation Bonus.