If your spouse was a non-resident alien for all of 2018 (did not live in the US more than 183 days, was not a citizen or green card holder), then you have two choices for your 2018 taxes.
You can file as married filing separately. You do not list your spouse as a dependent. If your spouse now has a tax number, enter it after their name but don't add their income. Married filing separately has the highest tax rates and many deductions and credits are reduced or disallowed.
Or, you can make an election to treat your spouse as a US person for tax reasons, in which case you can file as married filing jointly. Treating your spouse as a US person means you must report and pay US income tax on their income from anywhere in the world (there is an offsetting credit for foreign taxes they paid). You get lower tax rates and some other benefits by filing jointly, but the worldwide tax thing might cost you more than you save.
https://www.irs.gov/individuals/international-taxpayers/nonresident-spouse-treated-as-a-resident
