It's a bit more complicated than just reading the regs, you'd need to also look at some FAA legal interpretations and maybe AC's.

1. "121" means US 121 operator (technically 119 cert holder).

2. You do not need any 121 time to get a regional SIC job (or any airline actually).

3. You need 1000 hours 121 SIC to upgrade at a US airline, or to get hired as a DEC.
3a. You can substitute certain US 135 PIC, US 91K (fractional), or some US military time.

For you this is doesn't matter at al unless you want to get hired at a regional as a DEC. If you want to start as an FO like everybody else, all you need are ATP (or R-ATP) minimums.

What does matter is:
1. Do you have 1500 hours exclusive of the PC-12 time? If yes, and you meet the other ATP minimums, you can get a regional FO job now, and possibly a LCC major airline job right now.
2. If no, then you need to
2a. Verify, via the FAA, that your foriegn "135 equivalent" PC-12 SIC counts as FAA SIC/total time. I don't know OR
2b. Get a 91/135 job in the US and get your loggable time up to ATP mins. Good news, it's very easy to get those jobs right now.