Cross-border cooperation is still possible.
Article 32 of the Basic Law assigns relations with foreign countries to the federal level. Rhineland-Palatinate instead organises its own portfolios for matters such as interior affairs, finance and justice. Full ministry names may combine several responsibilities.
The state also maintains contacts beyond its borders. The State Chancellery coordinates relations with other states, the federal level and the European Union, among other matters. A state representation or responsibility for Europe is therefore not the same as having a separate foreign ministry.
The other three answers
The other three areas are represented in the state government.
Justice Minister
Justice is a state portfolio; the current ministry name combines justice and consumer protection. Administration of the justice system does not remove the independence of judicial decisions.
Finance Minister
The Finance Ministry belongs to the state government. It deals with state finances and the budget, so Finance Minister is not the missing office sought.
Interior Minister
Interior affairs are also a state portfolio. The current name combines interior affairs, integration and transport. Interior Minister is therefore not the answer to the question about the absent office.
No foreign minister does not mean no international powers at all.
Article 32(3) allows states to conclude treaties with foreign countries within their legislative responsibilities if the federal government consents. This limited possibility is part of the federal system, not a general independent foreign policy.
The question contains not. Look for the missing office rather than any ministry that exists. Changes to portfolio names or officeholders do not alter this fundamental distinction.
Article 32 · Basic Law ↗Foreign Minister → federal level; justice, finance and interior → also Rhineland-Palatinate.
The state’s international contacts are not a contradiction.
Three words for this question
- auswärtigforeign / external
- Here: relating to other countries.
- das Ressortministerial portfolio
- The area of responsibility assigned to a ministry.
- die Landesvertretungstate representation
- An office representing the federal state’s interests, for example at federal or EU level.