At a luncheon in honor of Nauru President Baron Divavesi Waqa, Tsai said the two countries are not only diplomatic allies but also members of the Austronesian language family.
In recent years, the two allies have developed deep links through cultural exchanges and cooperation in the areas of agriculture, medical care, clean energy, and education, one of the major channels for deepening friendship, she said.
For example, Tsai said, at the presentation of the first Distinguished Taiwan Alumni Awards last October, one of the seven outstanding overseas alumni winners was from Nauru.
On his part, Waqa said he was happy to be the first leader of an allied country to visit Taiwan this year and he also promised to strengthen bilateral relations through various cooperation plans.
He said the current cooperation programs between the two countries include coast guard patrol and he hoped to see the completion soon of agreements on search and rescue and cross-border crime prevention.
Nauru has benefited greatly from Taiwan's assistance on many fronts, Waqa said, expressing his thanks and hopes for the strengthening of bilateral ties through various cooperation plans.
Waqu also said his country will continue to work with Taiwan to ensure regional peace and to staunchly support Taiwan in the international community.
In a meeting with Waqa earlier in the day at the Presidential Office, Tsai reiterated that the Taiwan people had rejected the "one country, two systems" unification formula devised by China.
Opposition to that formula is a major consensus in Taiwan in 2019 and a common position among the ruling and opposition political parties, she said.
Tsai said that she believed that Waqa was aware of Taiwan's stance on cross-Taiwan Strait issues, which she had reiterated last week on behalf of the Taiwan people.
Taiwan thinks that sitting down at the negotiating table with the China government, without political preconditions, is the best way to resolve cross-strait issues, she said.
Based on that stance, Taiwan would work with like-minded international friends to make contributions to the world, Tsai said, thanking Waqa and his government for their support of Taiwan's efforts to gain wider international participation.
As a responsible country in the region, Taiwan will strive to ensure regional stability and promote regional prosperity and development, Tsai said.
She also thanked Waqa for his support of Taiwan at the 39th Pacific Islands Forum in Nauru in September 2018, saying that such interactions between the two countries have laid a solid foundation for bilateral relations.
According to Tsai, the Nauru Parliament last March passed a resolution that was proposed by Waqa to support Taiwan's campaign to participate in the United Nations system. It was the first time that Nauru was extending such support to Taiwan via legislation, she said.
Waqa has spoken out for Taiwan many times at the U.N. General Assembly and the U.N. Framework Convention on Climate Change, Tsai noted.
Her comments on the cross-strait issue came in the wake of Chinese President Xi Jinping's recent call for the two sides across the Taiwan Strait to adopt the "one country, two systems" model to resolve their conflicts.
The "one country, two systems" policy was first proposed by the late Chinese leader Deng Xiaoping in the early 1980s as way of reconciling the communist mainland with Taiwan, Hong Kong and Macau, which had capitalist economies.