Without seeing the poster in question, it is difficult to provide a detailed answer. However, based on the title and context provided, it can be inferred that the poster reflects the ideals of "internationalism" in the following ways:
The focus on a "trade union congress" suggests a coming together of workers from different countries, promoting international cooperation among workers.
The use of the word "international" suggests a global perspective and a belief in the importance of international relations and cooperation.
The manifesto may advocate for workers' rights and social justice issues that are not confined to national boundaries, emphasizing the need for international solidarity among workers.
Overall, the poster likely reflects a belief in the importance of international cooperation and solidarity among workers, as well as a recognition that social justice issues are global in scope and require international solutions.