Japan's currency is the strongest it's ever been. They are still a manufacturing super-power and exporter because they've had no inflation for a decade. That is the result of the BOJ maintaining a stable monetary base.
When there's no inflation, technological advances result in productivity increases that are reflected in lowered prices to consumers. This has enabled Japan (and Germany, too) to maintain their trade surplus even in the face of a rising currency.
Japan doesn't need to develop its internal economy. Its internal economy is just fine as evidenced by the high standard of living and low (4.6%) rate of unemployment. Its government spending, on the other hand, is ridiculous.