It is preferable for them to be in English, but it may be sufficient for them to be in the seller's own language, provided the buyer clearly understands that he is accepting the seller's conditions. If the retention of title clause works, the seller remains the owner of the goods and ownership will never have passed the buyer. If the buyer becomes insolvent, other creditors, including in particular the buyer's bank, may be in conflict with the seller. A liquidator or administrative receiver will wish to sell all available assets of the insolvent buyer to realise the bank's security or for the benefit of creditors generally. An effective retention of title clause will preserve the seller' title to the goods he has supplied.
Most clauses are variations of one of the above.
A simple retention of title clause seeks to preserve the seller's title to goods which remain unpaid and are in the seller's possession. Labelling his goods clearly. Making it a term of the contract that his goods are stored separately so that they can easily be identified. However an all monies clause is preferable. Such clauses will, in England, generally fail.