@ alya88, my understanding of the situation is as follows :
(a) you a US person ( citizen/ Green Card / Resident for tax purposes ) are living in the US
(b) you have income ( wages / self-employment etc. )
(c) your health insurance is through market place and covered through California state
(d) you plan to marry in Dec of this year ( Congratulations to you both )
(e) your spouse-to-be is a Non-Resident Alien, not present in the USA and therefore not required / eligible for health insurance coverage
(f) you are hoping to file jointly , using both your incomes ( total about US$ 50K )
By filing joint , you get the benefit of larger standard deduction, but also both the salaries/incomes would be taxed by the USA. Additionally, the spouse's income would be taxed in the country earned . It is unlikely that foreign tax credit ( for taxes the spouse paid to the other country ) would bring enough benefit. So why do you want to do it ? What benefit are you looking forward to ?
Additionally , as you mentioned recognition of the spouse's foreign income may affect your eligibility for govt. help for market place health insurance.
Please tell me more about this --- where is the spouse from ( and where is the earning from )? Have you already applied for K-visa for the fiance to join you here in the USA.
Or did you mean that your spouse-to-be is illegally here and therefore some of my assumptions are invalid ?
pk