Your mother, not you, needs to file a Form 709 for deeding the house in Vietnam to you, assuming the house (and all other gifts she may have given you) is valued more than $17,000, the annual exclusion amount for 2023. The gift tax return is always filed by the donor, not the recipient. For most regular folks, there is no gift tax due with the filing since the donor can use both the annual exclusion and lifetime exemption first ($12.92 million for 2023). If a Form 709 is required, make sure you keep a copy in your "permanent" file as you may need to submit another copy of the 709 with your mother's Estate Tax Return, Form 706, upon her demise, to the IRS. The fact that the house is located overseas is irrelevant. Your tax basis in the house is the same as your mother's as there is no step-up in tax basis for gifts, unlike inheritance.
See the Form 709 instructions on Who Must File.
https://www.irs.gov/instructions/i709
