That our garners may be full, affording all manner of store: that our sheep may bring forth thousands and ten thousands in our streets: That our garners, etc. - Our garners are full. These are not prayers put up by David for such blessings: but assertions, that such blessings were actually in possession. All these expressions should be understood in the present tense.
Ten thousands in our streets - בחצתינו bechutsotheynu should be translated in our pens or sheep-walks; for sheep bringing forth in the streets of cities or towns is absurd.