So let me get this straight:
• you have a L1 on Passport A and entered the USA on it
• while you’re in the USA you will be acquiring nationality B
• Country A doesn’t allow for dual nationality so you have to give up nationality A which you’re willing and planning to do
• however your L1 visa is attached to the passport from A, which you’re giving up
This is tricky as visas are issued onto passports through embassies in particular countries and are attached if not to the passport itself (they can often transfer when you get a new passport from the same country if it’s the same status) but to a passport class. So for example if you got a diplomatic passport, your old visa in a civilian passport wouldn’t work even if both are the same country. I’ve never heard of a visa transferable to another country’s passport.
I think your options are:
- Talk to an immigration lawyer. This is beyond the realm of internet stranger advice.
- Keep quiet about your dual nationality to Country A until you get a green card, which is independent of nationality once acquired. Countries do not normally know you’ve acquired a new citizenship unless you tell them or they have cause to investigate. So you’d keep using your passport A and visa in the A passport until you get a green card.
- Get a L1 visa in your new passport from Country B
- Don’t leave the USA while on the L1. The L1 is only used for entries. While you’re here,
you have the EAD which proves you have permission to work. So as long as you don’t leave the USA and want to return, you don’t have to get a new L1.
This is a rare outlier case as naturalizations rarely happen outside the naturalizing country (country B in this example). So best to see real professional advice.