Transatlantic Telecommunications Security Act This bill directs the Department of State and other federal agencies to help certain countries improve the security of their telecommunications networks and addresses related issues. Assistance provided under this bill shall be available to projects in a country that falls below certain gross domestic product per capita thresholds and is (1) a NATO member state that shares a border with Russia, or (2) a European country that has not participated in or aided Russia's invasion of Ukraine. A project located in such a country shall be eligible for assistance if the project (1) improves telecommunications networks; (2) is inclusive, transparent, economically viable, sustainable, supplied only with secure equipment and services, and compliant with international standards and laws; and (3) does not use equipment or services from China or Russia or replaces such equipment or services. To support eligible projects, the State Department shall provide diplomatic and political support and shall also encourage international financial institutions to provide investment support. The U.S. Trade and Development Agency, the U.S. International Development Finance Corporation, and other specified federal agencies shall also provide project support, such as feasibility studies and finance-related support, as necessary. The State Department must also appoint, from among its existing personnel, an International Telecommunication Union Security Campaign Director. The director must, among other duties, lead efforts to promote candidates for elections at the International Telecommunication Union who will support and defend democratic values, internet freedom, and telecommunication security.