There is no writing requirement, the price must be definite, there is a preference for specific performance, and an offer is more difficult to revoke. How will this be done - litigation or arbitration. Sovereign immunity - if contracting with a government a waiver should be obtained. An official language should be specified. Some countries require contracts to be in local language to be enforceable.
Notices are the method of officially notifying parties.
The performance by seller can be guaranteed by performance bond or Standby Letter of Credit. No fault, fault, liquidated damages. Import and foreign exchange licenses and other licenses may be necessary. Foreign firms may be prohibited from making direct sales. Representatives may have to register with government, or the representation agreements may need government approval.