求翻译：买方应于装运月份前30天，向卖方可接受的银行申请开具以卖方为受益人的不可撤消的即期信用证。至装运月份后第15天在日本议付有效。是什么意思？

Buyer shall 30 days prior to the month of shipment, the seller accepts the seller's bank for issuance of an order in favor of an irrevocable letter of credit at sight. To 15 days after shipment of the month in Japan, effective negotiation.

The buyer shall be 30 days prior to the Month shipment to the seller may accept the application for the Bank to the seller for the benefit of irrevocable letters of credit at sight. In the first 15 days after shipment from Japan in this effective.

The buyer should in the shipping month previous 30 days, the bank application which may accept to the seller draw up by the seller the immediate letter of credit which cannot be abolished for the beneficiary.15th days are effective after the shipping month in the Japanese negotiation.

Buyer shall be 30 days before the shipment month, acceptable to the seller to seller in favour of the banks for the opening of an irrevocable letter of credit. To ship on the 15th day of the month in Japan negotiate effectively.

Buyer shall 30 days prior to the month of shipment, the seller accepts the seller's bank for issuance of an order in favor of an irrevocable letter of credit at sight. To 15 days after shipment of the month in Japan, effective negotiation.